Combine the cranberry sauce, chili sauce, brown sugar, garlic powder, and black pepper in a large skillet or saucepan over medium heat and stir until the mixture is smooth and hot, about 5 minutes.
Add the frozen meatballs directly into the sauce and mix to coat them thoroughly.
Lower the heat to medium-low, cover the pan, and let the meatballs simmer gently for 15 to 20 minutes until they are fully heated.
Transfer the meatballs to a serving dish or keep them warm in a slow cooker.
Garnish with freshly chopped parsley or rosemary if you like, and serve warm.