Preheat oven to 350º F. Spray a 9x13" pan (or two smaller dishes) with cooking spray.
Brown beef and soften onion in a saucepan on the stovetop. Drain if needed. Dump into a large bowl.
Add tomato sauce, cabbage, rice, salt, pepper and garlic powder. Stir together and pour into prepared pan(s). Pour beef broth over the top of casserole. Do not stir. Cover with foil and bake for 1 hour.
Take off foil, stir, recover with foil and cook an additional 30 minutes, or until rice and cabbage is tender.
Serve as is or with a sprinkling of monterey jack cheese on top! Enjoy!