Preheat the oven to 400 degrees F and lightly grease a 9x13-inch baking dish.
Cut the tops off the bell peppers, remove the seeds, and arrange them upright in the baking dish.
Heat the olive oil in a large skillet over medium-high heat, then add the ground beef and diced onion, cooking until browned.
Stir in the minced garlic, diced tomatoes with their juices, cooked rice, and Italian seasoning, simmering for 5 minutes.
Mix in half of the fresh parsley and season with salt and pepper to taste.
Spoon the beef and rice mixture evenly into each bell pepper, packing them full.
Pour half a cup of water into the bottom of the baking dish, cover tightly with aluminum foil, and bake for 30 minutes.
Remove the foil, sprinkle with shredded cheese, and bake uncovered for another 15 minutes until the peppers are tender.
Garnish with freshly chopped parsley and serve warm.