Prepare the Veggies and Beans

1. Cook the Vegetables: In a large skillet over medium heat, sauté the diced onion, bell pepper, zucchini, and garlic until the vegetables are tender, about 5-7 minutes. Stir occasionally to prevent burning.
2. Add the Beans and Corn: Add the black beans, pinto beans, and corn to the skillet. Stir to combine and cook for an additional 2-3 minutes. If you’re using canned diced tomatoes with green chilies, add them now along with the salsa. Mix everything together.
3. Season: Sprinkle in the taco seasoning (or homemade seasoning mix) and stir to coat the vegetables and beans evenly. Taste and adjust seasoning with salt and pepper as needed. Remove from heat and set aside.

Assemble the Casserole

4. Prepare the Tortillas: If the tortillas are too large, cut them into quarters so they can fit better in the casserole dish. You can either leave them whole or cut them into pieces depending on the look and layering you prefer.
5. Layer the Casserole: In a greased 9×13-inch baking dish, start by placing a layer of tortillas at the bottom. Spread half of the veggie-bean mixture on top of the tortillas. Sprinkle with 1/2 cup of shredded cheese. Repeat the process with another layer of tortillas, the remaining veggie-bean mixture, and the rest of the cheese on top.
6. Bake: Cover the casserole with foil and bake in a preheated oven at 375°F (190°C) for 25-30 minutes, or until the cheese is melted and bubbly. For a golden top, you can remove the foil during the last 5 minutes of baking.

Garnish and Serve

7. Garnish: Once the casserole is out of the oven, sprinkle with fresh chopped cilantro for a burst of color and flavor.
8. Serve: Cut into squares and serve with sour cream, guacamole, or your favorite Mexican-style toppings.