Add the frozen meatballs to your slow cooker. There's no need to thaw them first.
Top with pineapple chunks, diced bell peppers, and onions.
In a large measuring cup or bowl, whisk together the juice from the pineapple can, brown sugar, granulated sugar, apple cider vinegar, ketchup, soy sauce, and cornstarch until well combined.
Pour the sauce mixture over the meatballs and vegetables in the crockpot.
Cover and cook on low heat for 3-5 hours or until the sauce has thickened and the meatballs are fully heated through.
Stir halfway through cooking time to ensure even heating.
Garnish with sliced green onions before serving.
Serve hot over rice or as an appetizer with toothpicks.
Notes
Slow Cooker Liner - Use a slow cooker liner for easier cleanup.
Sauce Thickness - If you need to speed things up after the meatballs are fully heated through, you can remove the lid and cook for 15-20 minutes on HIGH so the sauce thickens faster. Stir occasionally to make sure the sauce is not burning on the bottom.
Even Cooking - Stir the meatballs halfway through cooking to ensure they are evenly coated with sauce and heat evenly.
Appetizer Version - If serving only as an appetizer, you can choose to make it with just the sauce and omit the pineapple chunks, bell peppers, and onions. You'll still need to substitute the liquid from the pineapple can using ½ cup pineapple juice and ½ cup water.
Meatball Selection - Avoid using flavored meatballs that can throw off the flavor, such as Italian meatballs. This recipe works best with plain varieties like angus beef, homestyle, or even turkey or chicken meatballs.
Fresh Meatballs - If using fresh homemade meatballs, cooking times may vary slightly. Cook on LOW for 4-6 hours or until the internal temperature of the meatballs reaches 160-165°F.