Line an 8-inch square baking dish with parchment paper and lightly spray with cooking spray. If you don’t have cooking spray, you can grease the parchment paper with butter. Set the dish aside.
In a medium bowl combine crushed graham crackers, melted butter and brown sugar. Stir together with fork until the ingredients are combined. Press the crust firmly into the bottom of lined pan. Transfer to refrigerator to chill.
Add cream cheese and condensed milk to the bowl of a stand mixer. With the paddle attachment, beat on high until smooth and creamy. Add lemon zest and lemon juice. Mix until well combined.
In a small bowl add gelatin and boiling water. Whisk until completely dissolved. This should only take a couple of minutes.
Stir gelatin into the cream cheese mixture until well combined.
Pour filling over crust. Freeze until the filling is firm.