Crush the graham crackers to fine crumbs. Mix with melted butter in a bowl and press into a 9-inch pie dish.

In a large bowl, whisk sweetened condensed milk and fresh lemon juice until smooth. Fold in whipped topping until just combined.

Pour the lemon filling into the prepared crust and smooth out the surface. Sprinkle with lemon zest if desired.

Cover with plastic wrap and freeze for at least 4 hours, preferably overnight.

Let the pie sit at room temperature for 10 minutes before slicing, then serve immediately.