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    Home » Recipes » Sandwiches, Wraps, and Burgers

    Published: Mar 14, 2018 · Modified: Sep 5, 2022 by Willow Moon · This post may contain affiliate links. · As an Amazon Associate I earn from qualifying purchases. · I get commissions for purchases made through links in this post.

    Portobello Mushroom and Caramelized Onion Sliders

    Jump to Recipe Pin Video

    These sweet and savory Portobello Mushroom and Caramelized Onion Sliders will have you wanting more! Portobello mushrooms marinated in balsamic vinegar and Dijon mustard with sweet caramelized onions on your favorite bun, what's not to love! 

    Portobello Mushroom and Caramelized Onion Sliders close up.

    I have been wanting to make a portobello mushroom sandwich for the blog for awhile now. These Portobello Mushroom and Caramelized Onion Sliders are finally getting a debut because I was on a sandwich making kick recently.

    I fell in love with portobello mushroom sandwiches on my first trip with my husband. This was quite a few years before I knew I was gluten intolerant so there were more options for me eating out.

    On the trip I had three vegan portobello mushroom sandwiches at three different restaurants because they looked like the best choice on each of the menus.

    I was happy with every single one of them and not at all tired of eating the same thing several times on the trip.

    The ingredients that add a ton of flavor to the mushrooms are balsamic vinegar and Dijon mustard.

    Not only are the mushrooms marinated in balsamic vinegar and Dijon mustard, but they are also cooked down in the marinade as well.

    You may taste the mushrooms and think that the flavors are quite strong, but once you combine them with your favorite buns and some sweet caramelized onions, you will taste the symphony of flavors that the mushrooms become part of.

    Caramelized onions are one of those ingredients that elevate anything that you add them to. In fact, I would recommend doubling the amount so that you can use them in other dishes.

    Vegan Portobello Mushroom Sandwich open faced

    Tips

    • For caramelized onions you need some patience. It takes a good 40 minutes to get nicely browned onions. Slow and steady wins the race.
    • If the onions start to stick, add a little water, like a quarter of a cup or so.
    • Balsamic vinegar adds a wonderful flavor to caramelized onions. I always add a couple of splashes near the end of the cooking time.
    • Make a double batch of the caramelized onions and add them to a Vegan Caramelized Onion and Mushroom Grilled Cheese, a baked potato, or Vegan Mashed Cauliflower with Caramelized Onions and Mushrooms.
    • Make a double batch of the whole recipe and add half of it to pasta with the Maple Dijon Mayo and some steamed asparagus.
    • Cook mushrooms in marinade for more intense flavor.
    • The type of bread / buns that you use makes a big difference in the overall taste of the sandwiches.

    Other Vegan Sandwiches

    • Vegan Reuben Sandwich
    • Balsamic Roasted Vegetable Sandwich
    • BBQ Jackfruit Sandwich

    Portobello Sliders close up.

    Recipe

    The combination of flavors in these vegan portobello mushroom sliders is rich and satisfying. If you love this recipe, please come back and leave your feedback and star rating.

    Affiliate links below. We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.

    I used Pamela's pizza mix to make the buns. If you're vegan and gluten free like me, you're going to want to check it out. It's got a wonderful yeasty flavor.

    Pamela's pizza mix

    📋 Recipe

    Portobello Mushroom and Caramelized Onion Sliders
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    4.60 from 25 votes

    Portobello Mushroom and Caramelized Onion Sliders

    These sweet and savory Portobello Mushroom and Caramelized Onion Sliders will have you wanting more! Portobello mushrooms marinated in balsamic vinegar and Dijon mustard with sweet caramelized onions on your favorite bun, what's not to love! 
    Course Main Course
    Cuisine American
    Diet Gluten Free, Vegan, Vegetarian
    Prep Time 10 minutes minutes
    Cook Time 45 minutes minutes
    Inactive 1 hour hour
    Total Time 55 minutes minutes
    Servings 4 sliders
    Calories 329kcal
    Author Willow Moon
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    Ingredients

    Portobello Mushrooms

    • ½ cup balsamic vinegar
    • 3 tablespoons Dijon mustard
    • 2 tablespoons olive oil
    • 2 portobello mushrooms
    • Salt

    Caramelized Onions

    • 2 cups sliced onion
    • 2 tablespoons olive oil
    • 2 tablespoons balsamic vinegar
    • Salt

    Maple Dijon Mayo

    • ¼ cup vegan mayo
    • 2 tablespoons Dijon mustard
    • 2 tablespoons maple syrup
    • Buns - I used Pamela's gluten free pizza mix
    US Customary - Metric

    Instructions

    Caramelized Onions

    • Add olive oil to a hot pan. Add sliced onion and cook on medium-low heat for about 35-40 minutes, or until onions are caramelized. Add balsamic vinegar to deglaze the pan. Add salt. Remove onions.

    Portobello Mushrooms

    • Wipe mushrooms with a damp towel and slice into ½ " slices. Mix balsamic vinegar, Dijon mustard, and olive oil. Marinate the mushrooms for at least an hour.
    • In the same pan that you cooked the onions, place marinated mushrooms and marinade. Cook on medium heat until mushrooms are tender and marinade is cooked down.

    Maple Dijon Mayo

    • Mix all ingredients.
    • Slather Maple Dijon Mustard on buns. Add portobello mushrooms and caramelized onions.
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    Nutrition

    Calories: 329kcal | Carbohydrates: 24g | Protein: 2g | Fat: 23g | Saturated Fat: 3g | Cholesterol: 0mg | Sodium: 310mg | Potassium: 362mg | Fiber: 2g | Sugar: 16g | Vitamin C: 5.9mg | Calcium: 49mg | Iron: 0.9mg

    *Note: Nutrition information should be considered an estimate only. Different nutrition calculators give you different results. Also note that the buns were not calculated into the nutrition info.

    More Sandwiches, Wraps, and Burgers

    • Vegan Monte Cristo on a plate.
      Vegan Monte Cristo
    • Benedictine Tea Sandwiches on a plate.
      Benedictine Tea Sandwiches
    • Vegan BLT with Avocado
      Vegan BLT with Avocado
    • Vegan Reuben Sandwich on a cutting board.
      Vegan Reuben Sandwich

    Reader Interactions

    Comments

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      Recipe Rating




    1. Sienna says

      February 16, 2023 at 6:04 pm

      I enjoyed this greatly and found the recipe Delish just as it is!

      Reply
      • Willow Moon says

        February 17, 2023 at 10:56 am

        Thanks Sienna!

        Reply
    2. Sarah says

      January 15, 2023 at 7:06 pm

      Way, way too much balsamic in the marinade, and I found the combo of balsamic and dijon mustard off-putting. Others agreed. Next time I'll eliminate the dijon mustard, use half the balsamic, and figure out something to cut the vinegar a little, maybe more oil and/or water. I made a triple batch for a party (25 people) and it was not a hit. The caramelized onions were good and I would make those again.2 stars

      Reply
      • Willow Moon says

        January 16, 2023 at 10:33 am

        Hi Sarah, I'm sorry you didn't like them!

        Reply
    3. Emily says

      September 26, 2022 at 12:28 am

      I'd love to try these for an event...
      Can the mushroom/onion be made ahead of time and stored?

      Reply
      • Willow Moon says

        September 26, 2022 at 1:29 pm

        Yes, you can store them in an airtight container in the fridge for up to 5 days. If you worried about how they'll taste when reheated you might want to make some before the event and test it out.

        Reply
    4. Mary says

      November 28, 2021 at 2:13 pm

      Wow these were absolutely amazing..I will be making these again…thank you for sharing5 stars

      Reply
      • Willow Moon says

        November 28, 2021 at 2:49 pm

        Thanks Mary, I’m so glad you liked them!

        Reply
    5. Liz says

      May 13, 2021 at 6:59 pm

      Truly and absolutely delicious! I did add a little maple syrup while the mushrooms were cooling down as I found them to be a tiny bit too vinegary and that adjusted the flavors. Absolutely great!5 stars

      Reply
      • Willow Moon says

        May 14, 2021 at 9:51 am

        Thanks so much Liz! I'm glad you were able to tweak the recipe to your liking!

        Reply
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