Into a slow cooker, add the "marinara sauce” ingredients and whisk to combine.
Make meatballs:
Into a large mixing bowl, add all of the meatball ingredients and mix to combine.
With a spoon or cookie scoop, grab a small amount of the meatball mixture and roll into a meatball. Make 16 meatballs total.
Place each meatball in the slow cooker side by side on top of the marinara sauce.
Cook meatballs:
Slow cook on LOW for about 7 hours or until the center is no longer pink. OR cook on HIGH for 5 hours.
Make subs:
Once cooked, set the oven to broil.
Slice the hoagies in half lengthwise and place on a sheet pan. Scoop 4 meatballs with the sauce in each hoagie roll and sprinkle mozzarella cheese on top. Broil for 1-3 minutes or until the cheese is melty. Enjoy with a side salad!