Wash the bell peppers, cut off the tops, and remove seeds and membranes. Keep the tops for presentation if desired.

Heat olive oil in a frying pan over medium heat. Add chopped onion and minced garlic, sauté until translucent (~3 min). Add ground beef, cook until browned (~5 min). Mix in tomato paste, paprika, salt, and pepper. Simmer for 5 minutes.

Fill each pepper with the meat mixture, pressing down gently. Place stuffed peppers upright in a baking dish.

Preheat oven to 180°C (356°F). Bake the stuffed peppers for 30 minutes. In the last 5 minutes, sprinkle with grated cheese if using, and bake until melted and golden.

Remove from oven, sprinkle with chopped parsley, and serve hot.