Prep the mushrooms. Use a spoon to carefully scoop out and discard the gills and thick stems. Slice the mushrooms into ½-inch-thick strips and spread them out in a single layer in a baking dish. In a small bowl or measuring cup, whisk together the olive oil, soy sauce, chili powder, garlic powder and cumin until combined. Pour the mixture evenly over the portobellos, then carefully flip them over so that they are more or less evenly coated, and season with salt and pepper. Let the mushrooms marinate while you prepare the rest of the taco toppings and tortillas.

Cook the mushrooms. Heat 1 tablespoon olive oil in a large sauté pan over medium-high heat. Add half of the mushrooms and cook for 3-4 minutes per side, flipping once, until browned. Transfer the cooked mushrooms to a clean plate. Repeat with the remaining mushrooms.

Assemble the tacos. Fill each taco with a scoop of refried beans, a few slices of mushrooms and your desired toppings. Serve warm and enjoy!