Add the ground beef, onion, and oregano to a medium skillet, and cook over medium heat, breaking the meat up as it cooks, until meat is browned.
While the meat is cooking, prepare the rice according to package directions. Set aside.
Add cabbage, cooked meat, diced tomatoes, and tomato sauce to the crockpot, then sprinkle with salt and pepper, and pour in the beef broth. Cook on high for 2 hours.