Rinse bean sprouts under running cold water; drain. Cook and stir ham, onion and 1 tb margarine in 10-inch skillet until onion is tender. Stir in bean sprouts, spinach, water chestnuts and gingerroot; cook and stir 2 minutes. Stir in cornstarch and soy sauce.

Cut stack of phyllo leaves lengthwise into halves. Cut each half crosswise into thirds to make 30 squares, about 5 1/2 x 5 1/2 inches. Cover squares with waxed paper, then with damp towel to prevent them from drying out.

Heat oven to 350F. For each roll, use 2 phyllo squares. Place about 2 tb ham mixture slightly below center of square. Fold corner of square closest to filling over filling, tucking point under filling. Fold in and overlap the 2 opposite corners. Roll up; place seam side down on greased cookie sheet. Repeat with remaining phyllo squares. Brush roqls with 1 tb margarine. Bake until golden brown, about 25 minutes. Mix mustard and water until smooth; let stand 5 minutes. Serve with rolls. 15 appetizers; 75 calories per appetizer.

Do-ahead Tip: Before baking, place rolls on greased cookie sheet. Cover tightly with plastic wrap. Refrigerate up to 24 hours. Brush rolls with margarine. Bake in 350F oven until golden brown, about 25 minutes.