Preheat the oven to 350°F (175°C). Grease the baking dish with cooking spray or olive oil.
Remove the core from the cabbage and carefully peel off 12 large leaves, trying not to tear them. Blanch the cabbage leaves in boiling water for about 2-3 minutes until softened. Drain and set aside.
In a large skillet over medium heat, cook the ground beef, onion, and garlic until the beef is browned. Drain any excess fat.
Stir in the cooked rice, diced tomatoes, salt, black pepper, oregano, and paprika. Mix well to combine.
Lay out the blanched cabbage leaves on a flat surface. Place about ¼ cup of the beef mixture in each leaf and roll up tightly, tucking in the sides. Place the rolls seam-side down in the prepared baking dish.
Once all the rolls are in the dish, pour the tomato sauce evenly over the top. If desired, sprinkle shredded mozzarella cheese over the sauce.
Cover the baking dish with aluminum foil and bake in the preheated oven for 30 minutes. Remove the foil and bake for an additional 15-20 minutes, until the cheese is bubbly and golden.
Remove from the oven and let cool for a few minutes before serving.