Gather all the ingredients. Cut the tops off the bell peppers and remove the seeds and core. Dice the onion into small pieces.
In a large skillet, sauté the ground turkey until it's fully cooked. Add in the diced onion and cook until golden brown. Add sauce and let it simmer for 2-3 minutes.
Stir in parmesan and cottage cheese. Season with salt and pepper to taste.
Stuff peppers with the meat mixture. Place them side-by-side in a baking dish. Note: You'll want the peppers to touch so they hold each other upright while baking.
Cover the tops of the stuffed peppers with mozzarella cheese. Bake at 350°F for about 30 minutes, or until the tops turn golden brown and bubbly.