Whisk heavy cream, milk, and lemon pudding mix together in a bowl for 2 minutes. Let stand until soft-set, about 5 minutes. Pour pudding into the graham cracker pie crust.

Combine lemon frosting and whipped topping in the bowl of a stand mixer. Mix on medium speed for 2 minutes. Spoon over the pudding layer. Garnish with lemon slices and mint leaves.

Serve pie immediately or refrigerate for at least 1 hour for best flavor.