Preheat your oven to 375°F (190°C).
Slice the tops off the bell peppers and remove seeds and membranes.
Arrange the peppers upright in a baking dish.
Brown the ground beef in a skillet over medium heat.
Drain excess fat from the skillet.
Add onion and garlic to the skillet and sauté until onion is translucent.
Stir in cooked rice and drained diced tomatoes.
Season with salt, pepper, Italian seasoning, and Worcestershire sauce.
Fill each bell pepper with the beef and rice mixture.
Sprinkle shredded mozzarella on top if desired.
Cover the dish with foil and bake for 30 minutes.
Remove foil and bake for another 10-15 minutes.
Garnish with fresh parsley before serving.