In a large skillet over medium heat, add the 1 lb of lean ground beef. Cook until browned, breaking it apart with a spatula as it cooks. This should take about 5-7 minutes.
Once the beef is fully cooked, drain any excess fat if necessary. Sprinkle in the 1 (1.75-oz) packet of chili seasoning and stir to coat the meat. Next, add the 1 (8-oz) can of tomato sauce, 1 (15-oz) can of chili beans (with liquid), and 1 (15-oz) can of diced tomatoes (with liquid). Mix well and let simmer for about 5 minutes.
In a large mixing bowl, combine the 3 cups of cooked rice, 1 cup of cottage cheese, and 1 cup of sour cream. Stir until everything is evenly mixed.
Preheat your oven to 350°F (175°C). In your 9x13 inch baking dish, layer the rice mixture at the bottom. Spread the beef mixture evenly on top of the rice. Finally, sprinkle 1 cup of shredded cheddar cheese over the entire dish.
Cover the baking dish with aluminum foil and bake for 25 minutes. Remove the foil and bake for an additional 10-15 minutes, or until the cheese is bubbly and golden brown.
Once baked, remove from the oven and let it cool for a few minutes. Serve warm and enjoy this comforting Chili Sour Cream Rice Bake with your favorite toppings such as sliced jalapeños, fresh cilantro, or additional sour cream!