In A 2-Qt. Microwave-Safe Dish, Combine The Plum Sauce, Soy Sauce, Mustard And Ginger. Add Meatballs; Stir Gently To Coat. Cover And Microwave On High For 5-6 Minutes Or Until Heated Through, Stirring Once. Cool For 1 Minute. Fold In Onion And Cilantro.