Preheat your oven to 350°F (175°C) and spray a 13x9 inch baking dish with nonstick cooking spray.

In a large skillet, cook the ground beef over medium heat until browned, about 5-7 minutes. Drain excess fat and add chopped onion, cooking for another 3-4 minutes.

Sprinkle taco seasoning over the beef and onion, adding half a cup of water. Bring it to a boil, then reduce heat and simmer for 2-3 minutes.

Stir in black beans and diced tomatoes, then mix in sour cream. Let it cook for another 8-10 minutes on low heat.

Layer Fritos corn chips at the bottom of the baking dish.

Add half of the shredded cheese over the Fritos, followed by half of the beef mixture. Repeat layering with more Fritos, remaining beef, and top with the rest of the cheese.

Cover with aluminum foil and bake for 15 minutes. Remove the foil and bake for an additional 5 minutes until cheese is melted.

Let the casserole sit for a few minutes before serving with desired toppings.