Combine the ground turkey, Parmesan cheese, minced garlic, egg, breadcrumbs, Italian seasoning, and salt in a mixing bowl until evenly mixed.
Shape the mixture into 16 meatballs of similar size.
Pour half the marinara sauce into the bottom of the slow cooker, then add the meatballs in a single layer.
Cover the meatballs with the remaining marinara sauce.
Cook on low for 5 hours until the meatballs reach an internal temperature of 165°F.
Divide the spiralized zucchini noodles among four plates, top each with meatballs and sauce, and finish with chopped parsley.