Preheat oven to 350°F and spray a 9x13-inch baking dish with cooking spray.
In a large skillet over medium-high heat, brown the ground beef until fully cooked, about 8 minutes. Drain any excess fat.
Add taco seasoning and water to the beef. Stir and simmer for 3-4 minutes until thickened.
Remove from heat and stir in black beans, corn, Rotel tomatoes, sour cream, and 1 cup of shredded cheese. Mix until well combined.
Spread 2 cups of crushed Doritos in the bottom of the prepared baking dish to create a crunchy base layer.
Pour the beef mixture over the Doritos layer and spread evenly. Top with remaining 1 cup of cheese, then sprinkle remaining 1 cup of crushed Doritos on top.
Bake for 20-25 minutes until cheese is melted and casserole is heated through. Serve with your favorite taco toppings and watch it disappear!