Place graham cracker crumbs in a bowl and mix with sugar, salt, and melted butter. Press the mixture into a 9-inch pie plate. Make sure the mixture is even throughout the pie plate. Bake in the oven for 10 minutes. Remove from the oven and set aside.
In the meantime, in a bowl mix sweetened condensed milk, key lime juice, and key lime zest. Pour the mixture into the baked crust. Refrigerate for at least 3 hours.
Before serving, prepare whipped cream by adding cream, sugar, and vanilla in a metal bowl of a stand mixer. Whip the mixture starting on low speed and gradually raise the speed to medium high until cream forms medium to stiff peaks. Place cream in a pastry bag fitted with a star tip. Decorate pie with cream and decorate with lime slices. Serve.