Preheat the oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish or similar casserole pan.

Cook the aromatics. Heat olive oil in a large skillet over medium heat. Add the diced onion and cook until soft and translucent, about 4–5 minutes. Stir in the garlic and cook 30 seconds until fragrant.

Brown the beef. Add the ground beef to the skillet. Cook, breaking it up with a spoon, until no longer pink. Drain excess grease if needed.

Season and sauce. Sprinkle in the taco seasoning. Add the tomato sauce, black beans, corn, and green chilies. Stir and simmer 3–5 minutes to thicken slightly. Taste and add salt and pepper as needed.

Prepare the tortillas. For extra texture, lightly toast tortillas in a dry skillet for 30–60 seconds per side. This helps them hold up in the bake.

Layer the casserole. Place a layer of tortillas on the bottom of the baking dish, tearing as needed to cover. Spoon half the beef mixture over the tortillas. Sprinkle with a generous handful of cheese. Repeat with another tortilla layer, the remaining beef mixture, and another layer of cheese.

Optional creamy layer. If using, spread sour cream or Greek yogurt over the middle layer before adding cheese for a tangy, creamy bite.

Bake until bubbly. Cover loosely with foil and bake for 15 minutes. Remove the foil and bake another 8–10 minutes, until the cheese is melted and the edges are gently crisp.

Rest and top. Let the taco bake rest for 5–10 minutes to set. Add fresh toppings like cilantro, tomatoes, green onions, jalapeños, or avocado. Squeeze lime over the top if you like a bright finish.

Serve warm. Slice into squares and serve with extra sour cream, hot sauce, or salsa.