In a skillet over medium heat, season ground turkey with Italian seasoning, garlic powder, salt, and pepper. Cook the turkey until evenly brown. Set aside. Heat oil in the skillet, and cook onion, mushrooms, zucchini, red bell pepper, yellow bell pepper, and spinach until tender. Return turkey to the skillet. Mix in the tomatoes and tomato paste. Stuff the green peppers with the skillet mixture. Season with remaining salt, pepper and garlic powder to taste.
Put peppers in the oven, and cook 30 minutes or until peppers are at desired tenderness.