Preheat oven to 350 degrees. Grease an 8x8" pan with cooking spray.
In a small bowl, combine graham cracker crumbs, melted butter, sugar, and lime zest until the crumbs are moist.
Press the mixture firmly in to the bottom of the 8x8 pan, and bake for 10 minutes. Remove from the oven and let it cool completely.
After the pan has cooled, whisk together the egg yolks and sweetened condensed milk in a medium-sized bowl. Slowly add in the lime juice, and mix until it starts to thicken slightly.
Pour the lime filling over the graham cracker crust, and then top with coconut.
Bake for 15 minutes, or until just set.
Cool to room temperature and then refrigerate for at least one hour before serving.
You can also add fresh lime zest as a garnish. *Even though they are lime bars, they come out as a pale yellow color. You could add a drop or two of green food coloring if you wanted them to be darker.