Brown the Beef: In a large skillet over medium-high heat, cook the ground beef until no longer pink, breaking it apart with a wooden spoon as it cooks. Drain excess fat if necessary. Add one packet of taco seasoning along with the amount of water specified on the packet. Simmer for 3-5 minutes until the liquid is absorbed and set aside.
Mix the Casserole Base: In a large mixing bowl, combine the frozen hash browns, sour cream, fiesta cheese soup, can of tomatoes with green chiles (undrained), shredded Colby Jack cheese, melted butter, the second packet of taco seasoning, and the cooked taco-seasoned ground beef. Stir thoroughly until all ingredients are well incorporated.
Prepare for Baking: Spread the mixture evenly into a greased 9x13 inch baking dish. The consistency should be thick and well combined, creating a solid base for the topping.
Add Doritos Topping: Crush Doritos chips slightly and sprinkle them evenly across the top of the casserole mixture. This will create a delicious crunchy layer that contrasts with the creamy casserole underneath.
Bake to Perfection: Bake in a preheated 350°F (175°C) oven for 35-45 minutes, or until the edges are bubbling and the center is hot. The top should be golden brown and crispy. Let stand for 5 minutes before serving with additional sour cream on top.