In a large skillet over medium heat, add the lean ground beef. Cook until browned, breaking it apart with a spoon as it cooks, about 5-7 minutes. Drain any excess fat.
Once the beef is browned, stir in the taco seasoning and water. Let it simmer for about 2-3 minutes until the mixture is well combined and slightly thickened.
In a large mixing bowl, combine the cooked beef mixture with black beans, diced tomatoes and green chiles, tomato sauce, salsa, and cooked rice. Stir in the sour cream and 1 cup of shredded cheddar cheese until well mixed.
Preheat your oven to 350°F (175°C). Pour the mixture into a greased 9x13-inch baking dish, spreading it evenly.
Sprinkle the remaining 1 cup of shredded cheddar cheese over the top of the casserole.
Cover the baking dish with aluminum foil and bake in the preheated oven for 25 minutes. Then, remove the foil and bake for an additional 10-15 minutes, or until the cheese is bubbly and slightly golden.
Allow the casserole to cool for a few minutes before serving. Enjoy with your favorite taco toppings like chopped cilantro, avocado, or sliced jalapeños!