Preheat the oven to 350°F.
In a large skillet over medium heat, brown the ground beef or turkey with the diced onion and minced garlic until the meat is fully cooked. Drain any excess fat.
Stir in the diced tomatoes, tomato sauce, uncooked macaroni, water, Italian seasoning, salt, and black pepper. Bring to a boil, then reduce heat and simmer for about 10 minutes, stirring occasionally, until the pasta is tender.
While the pasta mixture is simmering, prepare the bell peppers by placing them cut-side up in a 9x13 inch baking dish.
Spoon the pasta mixture evenly into each halved bell pepper.
Sprinkle half of the Parmesan cheese over the filled peppers before covering with foil. Cover the baking dish with aluminum foil and bake for 30 minutes.
Remove the foil, sprinkle the mozzarella and the remaining parmesan cheese on top of the stuffed peppers, and return to the oven. Bake uncovered for an additional 10-15 minutes, or until the cheese is melted and bubbly.
Let cool for a few minutes before serving.