How to Make It
Preheat oven to 325°F. Stir together graham cracker crumbs, sugar, and butter in a medium bowl to combine. Press crumb mixture firmly into a lightly greased 9-inch pie. Bake in preheated oven until crust is golden brown, 18 to 20 minutes. Remove from oven, and let cool completely on a wire rack, about 30 minutes.
Stir together milk, lime juice, and lime zest in a large bowl until fully combined. Fold in 2 cups of the whipped topping. Transfer mixture to cooled pie crust, and chill at least 4 hours or overnight.
Fill a piping bag with remaining 1 cup whipped cream, and pipe a border along edge of pie. Top with lime slices.