
Preheat the broiler. Coat a baking sheet with cooking spray.
Place the ground beef, breadcrumbs, parsley, garlic, onion, egg, parmesan cheese, salt and pepper in a bowl. Mix until well combined. If it's hard to get everything to mix together, add a little water, a teaspoon at a time until a smooth mixture forms.
Shape the meat into 1 inch meatballs and place on the prepared baking sheet.
Broil the meatballs until browned, about 8-10 minutes.
Place the meatballs in the slow cooker. Add the marinara sauce, crushed tomatoes and tomato sauce and stir gently to combine.
Cover the slow cooker and cook on LOW for 6-8 hours or HIGH for 3-4 hours.
Top the meatballs with a sprinkling of parsley and parmesan cheese, then serve.