In 2-quart saucepan, mix sugar, cornstarch and salt. Gradually stir in water. Cook over medium heat, stirring constantly, until mixture thickens and boils. Boil and stir 1 minute; remove from heat. Stir in lemon peel, lemon juice, margarine and gingerroot. Press plastic wrap or waxed paper onto surface. Refrigerate about 4 hours or until chilled.