In a saucepan, combine the gelatin, sugar and salt. Add milk and egg yolks. Cook and stir over medium heat until mixture comes to a boil and gelatin is dissolved. Remove from the heat; add juices and zest. Chill until partially set.
Fold in whipped cream and chill until mixture mounds. Spoon into pie shell; chill thoroughly. Garnish with orange slices and mint if desired.