Place thawed meatballs into a 2-quart or larger slow cooker.
Whisk together cranberry sauce, ketchup, water, soy sauce, ground ginger, garlic powder, crushed red pepper flakes, and light brown sugar in a medium mixing bowl.
Pour the sauce on top of the meatballs. Cook on HIGH for 2 hours or on LOW for 4 hours.
Stir before serving. Garnish with dried cranberries and green onions if desired.