Preheat oven to 375°F. Lightly grease a baking dish large enough to hold the peppers upright.
Heat olive oil in a large skillet over medium heat. Sauté onion for 3-4 minutes until softened, then add garlic and cook for another minute.
In a large bowl, combine the turkey, cooked rice, diced tomatoes, ¾ cup cheese, sautéed onion and garlic, Italian seasoning, salt, and pepper. Mix well.
Stand the peppers upright in the prepared baking dish. Spoon the turkey mixture evenly into each pepper, packing it down gently.
Cover the dish with foil and bake for 25 minutes.
Remove foil, top each pepper with remaining cheese, and bake uncovered for another 10 minutes until peppers are tender and cheese is melted and bubbly.
Let cool for 5 minutes, garnish with fresh parsley if desired, and serve!