Preheat oven to 350 degrees F. Line an 8-inch metal baking pan with foil and spray foil with cooking spray.
Mix together the graham cracker crumbs, cinnamon, sugar, and melted butter. If you used unsalted butter, add a big pinch of salt as well. Press into the pan as tightly as you can and bake at 350F for 10 minutes.
In a mixing bowl, using an electric mixer on medium speed or a whisk, beat together condensed milk, egg yolks, lime juice and lime zest. Pour over the still-warm crust. Bake for about 14 to 16 minutes or until just barely set. If you have an instant read thermometer, the internal temp should top out between 170 and 175F.
Let cool completely, then cover and chill until very cold, preferably overnight.