Preheat oven to 350°F (175°C).
In a large skillet over medium heat, cook ground beef, diced onion, and minced garlic until the beef is browned and the onion is tender, about 7 to 8 minutes. Drain excess fat.
Add taco seasoning mix and 1 cup water to the skillet. Stir in diced tomatoes with green chilies. Simmer for 5 minutes until slightly thickened. Remove from heat.
In a large mixing bowl, combine the cooked beef mixture, sour cream, and salsa. Mix well.
Spray a 9×13 inch casserole dish with cooking spray.
Spread half of the crushed Doritos evenly on the bottom of the casserole dish.
Pour half of the beef mixture over the Doritos layer and spread evenly.
Sprinkle 1 cup of shredded cheddar cheese over the beef mixture.
Repeat layers with remaining crushed Doritos, beef mixture, and shredded cheddar cheese.
Cover the casserole tightly with aluminum foil.
To freeze: Place the covered casserole in the freezer. When ready to bake, thaw overnight in the refrigerator.
Preheat oven to 350°F (175°C). Bake the casserole, covered, for 20 minutes. Remove foil and bake for an additional 10 minutes or until cheese is melted and bubbly.
Let the casserole cool for 5 minutes before serving.