Preheat your oven to 350°F (175°C) and grease a 9x13 inch baking dish.

In a large skillet over medium heat, cook the ground beef, breaking it apart as it cooks. Add the diced onion and minced garlic. Cook for 5-7 minutes until the meat is no longer pink and the onions are translucent. Drain any excess fat.

Sprinkle in the taco seasoning, followed by the black beans, corn, and diced tomatoes with green chilies. Stir and let it simmer for 2-3 minutes.

In a separate bowl, combine the cream of mushroom soup and sour cream, whisking until smooth.

Layer half of the meat mixture in the baking dish, then spread half of the creamy soup mixture, followed by 1 cup of shredded cheese, and half a bag of crushed Doritos.

Repeat the layering process with the remaining meat mixture, creamy soup mixture, the rest of the crushed Doritos, and the remaining cheese.

Cover the casserole with aluminum foil and bake for 15 minutes, then remove the foil and bake for an additional 10 minutes until the cheese is bubbly and golden brown.

Let the casserole rest for 5-10 minutes before serving. Garnish with chopped green onions or sour cream if desired.