IN large bowl combine soup mix, sour cream and mayonnaise; stir in spinach, water chestnuts and green onions. Cover; chill at least 1 hour to blend flavors. Stir spinach mixture.
SPOON into melba rounds. Arrange 12 snacks at a time on microwavable plate.
HEAT. Microwave on High (100%) 45 seconds or until heated through. To Heat in Oven: Preheat oven to 400° F. Place prepared melba rounds on cookie sheet. Bake 5 minutes or until heated through.