Preheat your oven to 350°F (175°C) and lightly grease a 3-quart baking dish with nonstick spray.
Brown the ground beef in a large skillet over medium heat, about 6-8 minutes. Drain any excess grease.
Add onion and bell pepper to the skillet and cook until tender, about 5 minutes.
Stir in the taco seasoning and water. Simmer for about 5 minutes until thickened. Add the diced tomatoes, black beans, and sour cream, stirring to combine.
Layer 1 1/2 cups of the crushed Doritos at the bottom of the prepared baking dish.
Spread half of the meat mixture evenly over the Doritos layer. Sprinkle 1 1/2 cups of cheese on top.
Repeat the layers: Doritos, the remaining half of the meat, and another 1 1/2 cups of cheese.
Bake for 25 minutes, or until the cheese is fully melted and bubbly.
Top with chopped tomato, cilantro, and serve with salsa and additional sour cream on the side.