Stacked Fajita Vegetable Enchilada Casserole

Preheat oven to 350 degrees F (175 degrees C).

Place zucchini, red bell pepper, and 1 onion sliced into rings into a bowl; stir in 1 cup water, vegetable oil, and dry fajita seasoning. (Mixture can be left to marinate 1 to 2 hours, if desired.) Drain vegetables.

Heat vegetables in a large skillet over medium heat. Cook and stir until soft and slightly browned, about 10 minutes; transfer to a bowl and set aside.

Place flour, nutritional yeast, salt, garlic powder, and dry mustard powder into a saucepan and whisk in 2 cups water until thoroughly combined.

Place saucepan over medium heat and bring the mixture to a boil; reduce heat to low and simmer, whisking constantly until thick, about 5 minutes.

Stir in margarine and remove sauce from heat.

Pour 1/2 can of enchilada sauce into bottom of a 9x13-inch baking dish and spread the sauce out to cover the bottom. Top with 1/4 of the tortilla pieces, and spread 1/2 cup brown rice onto the tortillas.

Spread 1/3 of the cooked vegetables over the brown rice.

Spread 1 can of black beans over the vegetables; cover beans with 1/4 of the nutritional yeast sauce.

Repeat the layers twice more.

Make a final layer containing remaining 1/4 of the tortilla pieces, remaining nutritional yeast sauce, and remaining 1/2 can enchilada sauce.

Bake casserole in the preheated oven until bubbling, 30 to 45 minutes; allow to stand for 10 minutes.

Top casserole with optional black olives, avocado, tomato, jalapeno pepper, 2 tablespoons of chopped onion, salsa, and sour cream before serving.