Preheat the oven to 350°F (175°C).

In a large skillet over medium heat, add the ground beef (or turkey). Cook until browned, breaking it apart with a spatula as it cooks, about 5-7 minutes.

Once meat is cooked, add the diced onion and minced garlic to the skillet. Cook for another 2-3 minutes until the onion is translucent.

Stir in the taco seasoning, black beans, corn, and diced tomatoes. Mix everything thoroughly until combined and heated through, taking about 3-5 minutes.

In a large baking dish, begin layering: create a layer of crushed tortilla chips, followed by half of the meat mixture and then a layer of shredded cheddar cheese. Repeat with another layer of chips, meat mixture, and cheese.

Cover the dish with aluminum foil and bake in the preheated oven for 20 minutes. After 20 minutes, remove the foil and bake for an additional 10-15 minutes, or until the cheese is melted and bubbly.

While the casserole is baking, prepare toppings such as diced tomatoes, jalapeños, olives, and lettuce.

Once baked, let the casserole sit for about 5 minutes. Top each serving with sour cream and your choice of toppings before serving.