Preheat oven to 350°F (175°C).
In a large skillet, cook ground beef and onion over medium heat until beef is browned and onion is soft. Drain any excess fat.
Add chopped cabbage to the skillet and stir well.
Add uncooked rice, diced tomatoes, condensed tomato soup, garlic powder, salt, black pepper, and 2 cups of water to the skillet. Stir until well combined.
Bring the mixture to a boil, then reduce heat to low and simmer for 10 minutes.
Pour the mixture into a 9x13 inch baking dish.
Sprinkle grated Parmesan cheese over the top of the mixture.
Cut butter into small pieces and dot over the top of the cheese.
Cover the baking dish with aluminum foil and bake for 1 hour.
Remove the foil and bake for an additional 15 minutes, or until the cheese is golden brown.