Heat lemon juice, sugar, pineapple and syrup from the pineapple in a small saucepan. Stir occasionally and cook over medium heat, until mixture comes to a boil.
Mix together cornstarch and water to make a smooth paste. Stir into the pineapple mixture and cook over medium heat, stirring continually, until glaze thickens and turns clear. Remove from heat and cool. When cool, glaze can be spread.