Open the bag of Doritos slightly at the top. Use your hands to crush the chips into roughly 1-inch pieces. Scatter half of the Doritos in the bottom of a 13x9 inch dish.
In a large bowl, stir together the chicken, sour cream, chili powder, salt, and garlic powder. Spread over the Doritos.
Sprinkle the remaining Doritos on top, and cover with the cheeses.
Bake for 20 minutes, or until the cheese has melted and the casserole is warm throughout.
Notes
This casserole is best served warm from the oven. If you're only making this for 2–3 people, I recommend halving the recipe and baking it in an 8x8 inch pan. That said, if you want to reheat it, I recommend reheating it in the oven. The Doritos may not be as crisp as when originally baked.Substitutions/variations: you can use regular OR light sour cream. You can substitute Cool Ranch or even Flamin' Hot Doritos. You can substitute swiss, monterey jack, or pepper jack cheese.Want to add veggies? Add in 1 cup of canned corn and/or 1 cup of drained Rotel tomatoes to the chicken mixture. The chicken must be fully cooked before adding it to the casserole. You can use baked chicken breasts or thighs, rotisserie chicken, or packaged grilled chicken strips (chop them before adding to the casserole).