Sprinkle gelatin over juice in small cup; let stand until softened, 5 minutes. Place cup in small saucepan of simmering water; stir to dissolve gelatin.
Fold together yogurt, whipped topping, zest and dissolved gelatin in bowl. Refrigerate 30 minutes or overnight.
Meanwhile, combine strawberries and sugar in bowl. In 6 parfait glasses, layer equal amounts of berries and mousse; each should contain 2/3 cup berries and 2/3 mousse, total. Garnish with whipped topping, if desired.