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! 

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.

Balsamic Vinegar and Dijon Mustard Marinade

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

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.

Other Vegan Sandwiches You Might Like

• Vegan Reuben Sandwich
• Balsamic Roasted Vegetable Sandwich
• Roasted Cauliflower Steak Sandwich with Red Pepper and Black Olive Tapenade
• Smashed Chickpea and Avocado Sriracha Salad Sandwich

Tips for Making Portobello Mushroom and Caramelized Onion Sliders

• 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.

Portobello Mushroom and Caramelized Onion Sliders

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.

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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.

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4.6 from 5 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 vegan, gluten free

Keyword portobello mushroom sandwiches, vegan sandwiches

Prep Time 10 minutes

Cook Time 45 minutes

Inactive 1 hour

Total Time 55 minutes

Servings 4 sliders

Calories 329kcal

Author Willow Moon

Ingredients

Portobello Mushrooms

• 1/2 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

• 1/4 cup vegan mayo
• 2 tablespoons Dijon mustard
• 2 tablespoons maple syrup
• Buns - I used Pamela's pizza mix

US Customary - Metric

Instructions

• Portobello mushrooms: Wipe mushrooms with a damp towel and slice into 1/2 " slices. Mix balsamic vinegar, Dijon mustard, and olive oil. Marinate the mushrooms for at least an hour.
• 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: 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.

Nutrition

Calories: 329kcal | Carbohydrates: 24g | Protein: 2g | Fat: 23g | Saturated Fat: 3g | Cholesterol: 0mg | Sodium: 310mg | Potassium: 362mg | Fiber: 2g | Sugar: 16g | Vitamin C: 7.2% | Calcium: 4.9% | Iron: 4.8%

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*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.