Pour pineapple chunks with juice into a saucepan. Stir green bell pepper, brown sugar, cornstarch, soy sauce, and lemon juice through the pineapple chunks until sugar and cornstarch dissolve.
Bring the mixture to a boil; cook and stir until thickened, about 10 minutes.
Place meatballs into slow cooker crock; pour pineapple mixture over meatballs.
Cook on Medium for 2 hours, stirring every 30 minutes.
