Preheat the oven to 350 degrees and cover a baking sheet with parchment paper.
Put the mushrooms on the parchment paper, stem side down.
Brush the top of each mushroom with 1 teaspoon of rice bran oil, coating each cap entirely.
Sprinkle with hemp seeds and salt. Bake for 10 minutes, or until the mushrooms are browned and tender.
Remove the mushrooms from heat. Place them stem side up on a plate.
Put the mustard, Vegenaise, mashed avocado, and burger on top of one mushroom. Top the other mushroom with lettuce, onion, tomato, and sprouts.
Gather the two sides together and enjoy! If it’s too messy, enjoy with an old-fashioned fork and knife.