Add the frozen meatballs directly to the slow cooker and spread them into an even layer.
In a mixing bowl, combine the juice from the pineapple chunks with the cherry cola, barbecue sauce, brown sugar, Worcestershire sauce, garlic powder, onion powder, and cornstarch. Whisk until smooth and well combined.
Pour the pineapple chunks over the meatballs in the slow cooker.
Pour the sauce mixture over the meatballs and pineapple.
Gently stir everything together until the meatballs are fully coated and the sauce is evenly combined.
Cover and cook on LOW for 3 to 4 hours or on HIGH for 2 to 3 hours, stirring once or twice during cooking if possible.
For a thicker sauce, remove the lid during the last 20 to 30 minutes of cooking so the sauce can reduce.
Once the meatballs are heated through and coated in the thickened glaze, give everything a final stir and serve warm. Garnish with marachino cherries and parsley if desired.