Preheat oven to 350°F; spray a 9x13-inch dish with cooking spray.
Brown beef in a large skillet over medium-high about 8 minutes until fully cooked; drain excess fat.
Add taco seasoning and water; stir and simmer 3-4 minutes until thickened.
Off heat, stir in beans, corn, Rotel, sour cream, and 1 cup cheese until combined.
Spread 2 cups crushed Doritos in dish for a crunchy base.
Spread beef mixture evenly over chips; top with remaining 1 cup cheese, then remaining 1 cup crushed Doritos.
Bake 20-25 minutes until cheese melts and casserole heats through; serve with favorite taco toppings.