Mix the sauce: In a bowl, stir together barbecue sauce, the entire can of pineapple tidbits with juice, brown sugar, soy sauce, apple cider vinegar, garlic powder, onion powder, and red pepper flakes.
Load the cooker: Add frozen meatballs to the slow cooker.
Pour the sauce over the top and stir to coat evenly.
Cook low and slow: Cover and cook on Low for 4–6 hours, or on High for 2–3 hours, until the meatballs are heated through and the sauce is bubbly.
Thicken if needed: If the sauce seems thin, uncover and cook on High for 15–20 minutes, stirring once or twice, to reduce slightly.
Finish and season: Taste and add salt and pepper if needed. Stir in a handful of sliced green onions if you like.
Serve: Spoon over rice, tuck into slider buns, or set out with toothpicks. Sprinkle with sesame seeds for a nice finish.