Preheat the oven to 375 degrees Fahrenheit and coat a 2-quart baking dish with cooking spray.
Brown the ground beef over medium heat until it is almost completely pink. Cook for 3-4 minutes, or until the onions are soft. Stir in the taco seasoning and water thoroughly. Cook for a few minutes, or until slightly thickened.
Stir in the salsa and sour cream. Remove from heat after adding the black beans and corn.
Crush half of the corn chips coarsely and distribute evenly over the bottom of the baking dish, making sure to completely cover the bottom. Add the taco meat, followed by the cheese. Serve with the remaining corn chips on top.
Bake for 15-20 minutes, or until bubbling and cheese is melted. Uncover the casserole and bake for 5 minutes more. Remove from oven and sprinkle with desired toppings. Serve right away with additional salsa and sour cream on the side.