Add frozen meatballs to the bottom of your slow cooker.
Add all remaining ingredients (soup, broth, Worcestershire, ketchup, mustard, soy sauce, garlic powder, pepper) directly into the crockpot.
Stir everything together until the sauce is smooth and coats the meatballs.
Cover and cook: • On Low for 6–8 hours • Or High for 3–4 hours
(Optional) To thicken: Stir in a cornstarch slurry (1 tbsp cornstarch + 2 tbsp cold water) during the last 30 minutes and cook on high.