Crockpot Meatball Subs

1 package of frozen meatballs or precooked homemade meatballs
1 jar of marinara sauce
mozarella cheese slices
hoagie rolls

Place meatballs in the crockpot. Cover with marinara sauce. Heat on high for a couple of hours or on low for 4 hours. Once meatballs are done, place in hoagie rolls and top with mozzarella cheese.