Pour frozen meatballs into the bottom of the slow cooker.
In a small saucepan over medium heat, whisk together sauce ingredients until brown sugar is dissolved.
Pour sauce on top of meatballs.
Place lid on top of slow cooker and cook on LOW heat for 2-5 hours or until meatballs are warmed through.
You can serve these as-is like an appetizer or put them on top of cooked pasta or cooked rice for a yummy main dish.
Notes
It takes about 4-5 hours on low heat to cook frozen meatballs (or 2-3 hours on high heat). You can leave them in the warm setting for longer, but after a few hours they may start to toughen and become chewier.