To make this Turkey Parm Casserole gluten-free, replace the regular spaghetti with certified gluten-free spaghetti or another gluten-free pasta. Use gluten-free breadcrumbs in place of Italian breadcrumbs, and confirm that the ricotta, shredded turkey, garlic powder, Italian seasoning, spaghetti sauce, Parmesan, mozzarella, and fresh basil are gluten-free. If using leftover turkey, ensure it was not prepared with gluten-containing stuffing, gravy, marinades, or seasonings. Use clean cookware, utensils, and baking dishes to avoid cross-contamination.