In a large bowl, combine the ground turkey, breadcrumbs, Parmesan cheese, onion, garlic, parsley, egg, salt and pepper. Mix well using your hands or a large spoon until all ingredients are evenly distributed.
Shape the turkey mixture into meatballs, about 1 1/2 inches in diameter. You should have around 20-24 meatballs.
Pour half of the marinara sauce into the bottom of a 6-quart slow cooker.
Place the turkey meatballs in a single layer on top of the sauce in the slow cooker.
Pour the remaining marinara sauce evenly over the meatballs.
Cover the slow cooker and cook on low for 4 hours, or until the meatballs are cooked through and have reached an internal temperature of 165°F.
Gently stir the meatballs to coat them evenly with the sauce. Garnish with chopped fresh basil, if desired.
Notes
Breadcrumbs help bind the meatballs together and add texture. You can use plain or Italian-seasoned breadcrumbs, it doesn’t matter. The seasoned breadcrumbs will give you more flavor.