1. Preheat the oven to 375°F (190°C).

2. In a large skillet, cook the ground beef until browned. Drain any excess fat.

3. Add condensed cream of mushroom soup, cream of mushroom soup, rotel tomatoes, diced tomatoes, and 2% low-fat milk to the skillet. Stir to combine and simmer for 5 minutes.

4. Cook the fettuccine according to package instructions. Drain and set aside.

5. In a separate bowl, mix together shredded colby cheese, sour cream, and mashed potatoes until well combined.

6. In a baking dish, layer half of the cooked fettuccine on the bottom. Top with the beef and mushroom mixture. Add the remaining fettuccine on top.

7. Spread the mashed potato mixture over the fettuccine layer.

8. Bake in the preheated oven for 25-30 minutes, or until bubbly and golden brown on top.

9. Serve hot and enjoy!