To a medium mixing bowl, add the lemon pudding mix, milk, and lemon juice. Mix for 1 minute using a hand mixer until thickened.
Spoon approximately 2/3 of the lemon pudding mixture into the pie crust and spread into an even layer.
Add 2 ounces (about ¾ cup) of Cool Whip to the bowl with the remaining lemon pudding. Fold together until evenly combined to make a lemon mousse.
Spoon the mousse into the pie crust and spread over the lemon pudding layer. Then top with the remaining Cool Whip and spread it over the pie.
Allow the pie to chill in the fridge to set up for 2 hours or longer. Sprinkle some lemon zest over the top of the pie and cut it into 8 slices before serving.