In a crockpot combine meatballs, onion, brown sugar, soup mix and Coke. Cover and cook on low for 3.5 to 4.5 hours or until heated through.
Place meatballs on each bun bottom and sprinkle with 1/4 C shredded cheese. Place on baking sheets and broil for 2 minutes or until cheese is melted. Replace bun tops and serve!