In a small saucepan, combine the rhubarb, 2 tablespoons sugar and water. Bring to a boil, stirring constantly. Reduce heat; simmer, uncovered, until tender, about 10 minutes. Transfer to a small bowl; cool to room temperature.
Place strawberries and remaining sugar in a food processor; cover and process until pureed. Stir into rhubarb mixture. Fold in whipped cream. Spoon into 2 parfait glasses or dessert dishes. Cover and refrigerate until chilled. Garnish with additional berries if desired.
Editor's Note: If using frozen rhubarb, measure rhubarb while still frozen, then thaw completely. Drain in a colander, but do not press liquid out.