I had a request and a few questions about the cake, so here's the deal:
I don't have the exact recipe, but as near as I can tell, you use cake mix to make two round pans of white cake and one of chocolate. That'll be your buns and patty.
Slice kiwis and strawberries, and add yellow food coloring to Cool Whip. That's the pickles, tomatoes, and cheese (or, if you prefer, special sauce, a phrase that has always bothered me a little, so let's say it's cheese). Then maybe get some white frosting for mayo. Let the cakes cool, and arrange everything so it looks like the picture below. Sprinkle a few poppy seeds on top for extra bun effect. Finally, call and invite me over so I can make sure you did it right.