**Preheat the Oven**
- Preheat your oven to 350°F (175°C).
**Cook the Meat**
- In a large skillet, cook the ground beef and diced onion over medium heat until the meat is browned and fully cooked. Drain any excess fat.
**Season the Meat**
- Add taco seasoning and water to the skillet. Stir well and let it simmer for 2–3 minutes.
**Prepare the Sauce**
- In a mixing bowl, combine the salsa, cream of chicken soup, sour cream, and 1 cup of shredded cheddar cheese. Mix until smooth.
**Layer the Casserole**
- Spread a layer of crushed Doritos on the bottom of a 9x13-inch casserole dish. Add half of the cooked meat mixture, followed by half of the sauce mixture. Repeat the layers, ending with a final layer of crushed Doritos on top.
**Top with Cheese**
- Sprinkle the remaining 1 cup of shredded cheddar cheese evenly over the top.
**Bake**
- Bake in the preheated oven for 25–30 minutes, or until the cheese is melted and bubbly.
**Serve**
- Remove from the oven and let the casserole cool slightly. Garnish with optional toppings and serve warm.