Preheat your oven to 375°F (190°C).

Cut the tops off each bell pepper, remove the seeds and rinse under cold water.

In a large skillet over medium heat, add olive oil and sauté chopped onion and minced garlic for 3-4 minutes until translucent.

Add the ground beef to the skillet, cook for 5-7 minutes until browned.

Stir in cooked rice, tomato sauce, diced tomatoes, Italian seasoning, salt, and pepper. Simmer for 5 minutes.

Stuff each bell pepper with the mixture and place upright in a baking dish.

Add about 1/4 inch of water to the baking dish, cover tightly with aluminum foil, and bake for 35 minutes.

Remove foil, sprinkle mozzarella cheese over the top, and bake uncovered for an additional 10-15 minutes until cheese is melted.

Let the peppers rest for a few minutes, garnish with fresh parsley, and serve warm.