Line an 8" square baking dish with parchment paper, spray with cooking spray and set aside.

Pulse graham crackers in a food processor until they are fine crumbs, then mix in brown sugar and salt. Stir in melted butter and mix until butter evenly coats crumbs and the mixture resembles damp sand.

Spread mixture into prepared pan then press firmly into an even layer using a flat-bottomed cup.

Beat cream cheese and sweetened condensed milk in a large bowl or the bowl of a stand mixer fitted with whip attachment. Add in zest and lemon juice and mix until completely combined.

Pour boiling water into a small bowl and add gelatin while whisking to avoid lumps. Whisk until completely dissolved. With mixer on medium speed, slowly drizzle gelatin into cream cheese mixture and mix until completely incorporated.

Pour lemon cream cheese mixture over crust and spread evenly. Cover with plastic wrap and chill for at least 4 hours or overnight. Cut into squares and serve cold with a sprinkling of freshly grated lemon.