Preheat your oven to 350°F (175°C).
In a large skillet over medium heat, cook the ground beef until browned. Drain excess fat.
Stir in the taco seasoning according to the package instructions, adding some water if needed. Mix well.
In a large mixing bowl, combine the cooked beef, black beans, diced tomatoes, and 1 cup of shredded cheese.
In the bottom of a 9x13 inch baking dish, create a layer of Doritos (about half of the bag).
Spoon half of the beef mixture over the Doritos and dollop half of the sour cream on top.
Repeat the layering process with the remaining Doritos, beef mixture, and sour cream.
Finish by topping with the remaining shredded cheese.
Cover the baking dish with aluminum foil and bake in the preheated oven for 20 minutes.
Remove the foil and bake for an additional 10 minutes, or until the cheese is melted and bubbly.
Let the casserole cool for a few minutes before serving. Top with optional toppings if desired.