Preheat oven to 350 degrees F.
Place peppers in baking dish and cover with aluminum foil. Bake 15 minutes in the preheated oven.
Meanwhile, in a skillet over medium-high heat, cook the turkey until evenly brown; set aside.
Heat oil in the skillet over medium heat and cook onion, zucchini, carrots and mushrooms until tender, approximately 8-10 minutes.
Return turkey to the skillet with vegetables. Add the tomatoes and tomato sauce, Italian seasoning, garlic powder, salt and pepper.
Stuff the green peppers with the skillet mixture.
Cover with foil again and return peppers to the oven, and continue cooking 35-40 minutes.