Preheat oven to 375°F and set aside a casserole dish (I used a square 8x8" dish).
To make the enchilada sauce, throw everything in a blender and blend on high until well combined. The sauce may be a little chunky but that's okay.
Cook the onions over medium heat until translucent, then add zucchini and mushrooms and continue to cook until zucchini is tender. Add nutritional yeast if using, then mix in black beans and take off heat.
Assemble the enchilada lasagna by first spreading a thin layer of sauce on the bottom of your casserole dish. Then add the tortillas, overlapping them or cutting them so they cover the bottom of the dish entirely. Spoon over the veggie/bean filling and sprinkle with cheese. Top with enchilada sauce and repeat.
You should be able to make two layers of filling. Top your final layer of filling/cheese with tortillas, spread with enchilada sauce, and sprinkle with remaining cheese. Bake for 20 minutes. Cool briefly before slicing into them, but serve while still warm.