How to Make It
Preheat oven to 400°F. Toss together mushrooms, oil, tamari, salt, and pepper on a large rimmed baking sheet and spread in an even layer. Bake until mushrooms are browned and crisp around the edges, 20 to 25 minutes, flipping once halfway through cook time.
Build sandwiches with mayonnaise, mushrooms, lettuce, and tomato.