Preheat your oven to 350°F (180°C)
Prepare a 2-quart casserole dish by spraying it with nonstick cooking spray.
Combine chicken, cheese, sour cream, milk, cream of chicken soup, Rotel tomatoes, and taco seasoning in a bowl and mix well.
Spread half of the chicken mixture in a 2-quart casserole dish, top with a layer of Doritos, approximately 2 cups then spread the rest of the chicken mixture on top of the Doritos.
Sprinkle an additional cup of shredded cheddar cheese over the top of the casserole.
Cover the casserole with foil and bake for 35 minutes in a preheated oven set to 350 degrees Fahrenheit.
If you want to make more servings, double the recipe and bake in a larger 9x13-inch baking dish for 45 minutes.
Serve the Mexican white trash recipe immediately, Mexican style!