1. Preheat the oven to 350°F (175°C).
2. Grease a 2-quart casserole dish and set aside.
3. In a large bowl, mix together the shredded chicken or cooked ground beef, shredded cheese, cream of chicken soup, Rotel tomatoes, sour cream, milk, and taco seasoning until well combined.
4. Crush the Nacho Doritos into bite-sized pieces.
5. Spread a layer of crushed Doritos in the bottom of the prepared casserole dish.
6. Add half of the filling mixture over the Doritos layer.
7. Repeat the layers by adding another layer of crushed Doritos followed by the remaining filling mixture.
8. If desired, sprinkle additional shredded cheese on top for extra cheesiness.
9. Cover the casserole dish with aluminum foil and bake for 35 minutes.
10. Remove the foil and bake uncovered for an additional 10 minutes to create a crispy top.
11. Let the casserole cool for a few minutes before serving.
12. Serve warm and enjoy with a side salad or steamed vegetables.