1
Preheat oven to 375 °F.
2
Chop onion. In a large skillet, sauté onion in olive oil over medium heat until onion begins to soften, about 5 minutes. Set ½ sautéed onion aside in a large bowl.
3
Stir tomato sauce, beef broth, balsamic vinegar and red pepper flakes into the skillet; cook for about 1 minute until heated through. Pour tomato sauce mixture into a large baking dish and set aside.
4
Combine breadcrumbs, ground turkey, sausage, diced tomatoes, chopped parsley, minced garlic, and cayenne pepper into the large mixing bowl with the sautéed onions; mix to combine well. Stir in ½ parmesan cheese. Set meat mixture aside.
5
Slice the peppers in half and discard the membranes. Stuff each half of the peppers with the meat mixture and place inside the baking dish with the tomato sauce. Sprinkle the remaining Parmesan cheese over the stuffed peppers. Cover the baking dish with aluminum foil and bake for 45 minutes.
6
Remove aluminum foil and bake another 20-25 minutes until the meat is cooked through and the cheese is bubbly.
7
Enjoy peppers topped with tomato sauce.