1. Preheat the oven to 350°F.
2. Cut the bell peppers in half, remove seeds and ribs but leave the stem. Stand the peppers up inside a large casserole dish.
3. In a large skillet, heat the olive oil over medium heat. Add the onion and cook, stirring occasionally, until tender and browning around the edges, about 8 to 10 minutes. Stir in the garlic and cook 2 minutes more.
4. Add ground beef and cook until browned, about 10 minutes, stirring and breaking up any chunks with the back of a spoon while cooking. Stir in the diced tomatoes, tomato sauce, cooked rice, parsley, Italian seasoning, salt, and pepper. Cook, stirring occasionally, until the mixture is heated through, about 3 minutes. Remove from the heat. Fold in 1 cup mozzarella cheese.
5. Spoon the filling into the peppers. Sprinkle the filling with the remaining 1/2 cup cheese.
6. Bake for 20 minutes or until the peppers are tender and the cheese is starting to brown. Let cool for about 5 minutes before serving. Garnish with fresh parsley, if desired. Serve and enjoy!
