In a large bowl, whisk together the milk and pudding mixes for 2 minutes until thick and smooth.
Pour in the thawed lemonade concentrate and whisk for 1-2 more minutes until fully incorporated and lemon-flavored.
Fold in the thawed whipped topping until no streaks remain.
Pour the lemonade pie filling into the graham cracker crust, smoothing it into an even layer.
Refrigerate for at least 4 hours until completely set and chilled.
Garnish with lemon slices and candied lemon peel if desired.
For a frozen lemonade pie, place it in the freezer for 2-3 hours before slicing and serving.
