Cook rice according to package directions or your preferred cooking method. Set aside to cool.
Preheat oven to 400 degrees F.
Cut the tops off the peppers and remove seeds and membranes.
Heat olive oil in a large skillet over medium heat. Add the onion and cook until it starts to soften, 2-3 minutes.
Add the ground turkey (or beef) to the pan and cook, crumbling, until browned and no longer pink. Add the garlic and cook, stirring for 30 seconds.
Add the diced tomatoes, tomato sauce, Italian seasoning, garlic powder, salt and pepper to the pan. Reduce heat to low and simmer, stirring for 2-3 minutes. Remove pan from the heat and stir in the cooked rice and half of the cheese.
Pour ½ cup of water into a 9x13-inch baking dish. Fill bell pepper halves with the meat and rice mixture (about 1 cup of filling per pepper) and place in the baking dish. Sprinkle on the remaining shredded cheese.
Cover with a piece of aluminum foil that you have lightly sprayed with cooking spray to prevent sticking. Bake for 30 minutes, uncover, and bake 5 minutes more, until cheese is lightly browned and filling is hot. Serve.