Preheat the oven to 350 degrees F (175 degrees C).

Bring a large pot of water to a boil. Add cabbage strips to boiling water. Boil until tender. Drain.

Meanwhile, heat a large skillet over medium-high heat. Cook and stir beef and onion in the hot skillet until beef is browned and crumbly, 5 to 7 minutes. Drain and discard grease.

Mix together meat and onion mixture with cooked rice, cabbage, tomato sauce, diced tomatoes, cabbage, salt, and pepper until well combined. Place mixture into a large glass baking dish.

Bake in the preheated oven until bubbly and heated through, 30 to 45 minutes.