Pour half the sauce in a 8 quart slow cooker.
Place eggs in a large bowl and whisk, add breadcrumbs, minced onion, parsley, garlic, salt, oregano, black pepper and stir to combine. Add in the chicken and mix with your clean hands.
Form 1 1/2 inch meatballs and place in the slow cooker. Pour leftover sauce all over the meatballs and cover and cook on low for 6-7 hours.
5 minutes before serving, place 2 mozzarella slices over however many meatballs you’d like on your buns, cover with lid and wait until slightly melted, scoop out with a large spoon and place on the buns! Sprinkle with parsley (optional) and enjoy! OR You place the meatballs ontop of the sub directly.