Cook the Meat: In a large skillet, heat the olive oil over medium heat. Add the diced onion and garlic, cooking until the onion becomes translucent (about 5 minutes). Add the ground beef or turkey, cooking until browned. Drain any excess fat.
Season and Add Ingredients: Stir in the taco seasoning mix, black beans, corn, diced tomatoes with green chilies, and enchilada sauce. Simmer for about 5 minutes to let the flavors combine. Season with salt and pepper to taste.
Assemble the Casserole: In a 9×13 inch baking dish, spread a thin layer of the meat mixture. Place a layer of tortilla quarters over the meat, then sprinkle with a portion of the shredded cheeses. Repeat the layers, finishing with a generous layer of cheese on top.
Bake: Cover the baking dish with foil and bake in the preheated oven for 20 minutes. Remove the foil and bake for an additional 10 minutes, or until the cheese is melted and bubbly.
Serve: Let the casserole cool for a few minutes before serving. Top with your choice of optional toppings such as sour cream, chopped cilantro, sliced jalapeños, diced avocado, and lime wedges.