In a cup of boiling water, add gelatin and sugar. Stir for 2 minute or until gelatin is dissolved. Stir in cold water and lemon juice. Chill for about 30 min., or until the mixture is the consistency of unbeaten eggwhites.
Fold in yogurt, whipped topping, lemon rind (if desired) and lemon zest (if desired) into gelatin mixture, then spoon into pie crust. Chill at least 3 hours.
Alternatatively the mixture can be spooned into 12 single serve graham cracker crusts (these can easily be packed in lunches).