Preheat the oven to 350 degrees.
Grease and flour a 9 X 13 inch dish, and set aside. In the mixing bowl of a stand mixer, mix the Lime Jello, sugar, flour, salt, baking powder, and baking soda, until completely blended.
Add the oil, Key Lime Juice, vanilla, eggs, and lime green food coloring.
Mix until well blended.
Scrape down the sides of the mixing bowl, and blend one more time.
Pour the batter into the greased and floured 9 X 13 dish.
Bake for 25 to 30 minutes, or until a toothpick inserted in the center comes out clean.
Remove the cake to a wire rack to completely cool.
When the cake is cooled, make the icing.
Cream together the butter and cream cheese, until smooth and creamy.
Add the powdered sugar, a little at a time, until all the powdered sugar is added, and mixing between additions.
Mix until the icing is smooth and creamy.
Add a few drops of lemon juice at the very end of mixing, just to give the icing a fresh flavor.
Ice the cake with the icing, and sprinkle a few crushed graham cracker crumbs on top - or you can top with green sugars.
Add a slice of lime, serve, and Enjoy!