Preheat oven to 350°F. Combine graham crumbs and melted butter; press into the bottom of two greased 8-inch cake pans.

Prepare cake mix according to package directions and pour over the graham crusts.

Bake for 22–26 minutes until a toothpick comes out clean. Cool completely.

Beat cream cheese and condensed milk until smooth. Stir in lime juice and 1 tbsp zest.

In a separate bowl, whip heavy cream and powdered sugar until stiff peaks form. Fold half into the lime mixture.

Layer the cakes with lime filling in the middle and on the exterior.

Pipe remaining whipped cream on top and garnish with lime slices and remaining zest.

Chill for 4 hours before serving.