In a large bowl, combine the ground turkey, oats, half of the tomato sauce, onion, zucchini, garlic, egg, salt, black pepper, and Italian seasoning. Use your hands to mix well.
Shape the mixture and place it in a greased 8x4 bread loaf pan. Place the pan inside your slow cooker (if a loaf pan doesn’t fit inside your slow cooker, shape the meatloaf into a large football and place it in the middle of the slow cooker, trying not to touch the sides).
Spoon the remaining tomato sauce over the top of the meatloaf.
Cover and cook on low for 6 hours (or, high for 4 hours) until the meatloaf reaches an internal temperature of 160 degrees F.