Mix vegan mayo, ground mustard, mustard seeds, lemon juice, lemon zest, maple syrup, and salt and pepper in a bowl.
Slice tofu into cubes (or mash) and add to the dressing. Add roasted cashews, chopped celery, red onion, and tarragon. Mix together.
Serve on lettuce leaves, in a wrap or sandwich.
Notes
Zest lemons before juicing.If you let this sit overnight, the flavors will meld and taste even better the next day.This recipe will last 5 days in an airtight container in the fridge. I suggest adding it to a sandwich right before you want to eat it. If you want to make it in a sandwich ahead of time, I would do it the day before, but no longer.