Before You Begin
Prepare your slow cooker and ingredients as needed. Cooking times and results may vary depending on your equipment and ingredients.
Add ketchup, brown sugar, and liquid smoke (or soy sauce) to the slow cooker. Stir until well combined.
Add the minced onion and frozen meatballs. Stir gently to coat the meatballs evenly.
Cook on HIGH for about 2 hours until meatballs are heated through, hot and bubbling, and reach 165°F (74°C).
Stir gently before serving to redistribute the sauce.
Switch the slow cooker to WARM if holding for serving.