Preheat oven to 375°F (190°C). Arrange bell peppers cut side up in a baking dish.
Heat olive oil in a large pan over medium heat. Sauté onion until soft, then add garlic and cook for 1 minute.
Add ground beef and cook until browned, breaking it apart as it cooks.
Stir in cooked brown rice, diced tomatoes, tomato paste, oregano, and paprika.
Simmer for 4–5 minutes until slightly thickened. Season with salt and pepper.
Fill each pepper with the mixture.
Bake for 10–12 minutes until peppers begin to soften.
Sprinkle cheese over the tops and bake for another 5–7 minutes until melted.
Garnish with parsley and serve warm.