Cook the Meat Mixture: In a pan, heat olive oil over medium heat. Add the diced onion and cook until softened. Add the ground beef or turkey and cook until browned. Stir in taco seasoning, tomato sauce, black beans, and corn. Simmer for 5 minutes.
Assemble the Bake: Preheat the oven to 180°C (350°F). In a greased baking dish, layer tortillas, meat mixture, and cheeses. Repeat until all ingredients are used, ending with a cheese layer on top.
Bake: Place the dish in the oven and bake for 20-25 minutes or until the cheese is melted and bubbly.
Serve: Let it cool for a few minutes before slicing. Garnish with fresh herbs, sour cream, or avocado slices for extra flavor.