In a slow cooker, combine the barbecue sauce, sweet and sour sauce, soy sauce, garlic powder, onion powder, black pepper, and red pepper flakes if using. Stir well to combine.
Add the frozen meatballs to the sauce mixture, ensuring they are well coated.
Add the pineapple chunks, gently mixing them into the meatballs and sauce.
Cover the slow cooker and cook on low for 4 to 6 hours or on high for 2 to 3 hours, until the meatballs are heated through and the sauce is bubbly.
Once cooked, stir the meatballs gently to coat them in the sauce before serving.
Garnish with chopped green onions for added flavor and presentation.