Info on the nacho-platter cake comes from Happiest Hour columnist Marti Jonjak, who executed the mexi-treat with her friend Ceair:

Nachos = pie crust, cut into triangular wedges & baked
Ground beef = chocolate cake. We made extra and crumbled it around so it looked like a spilling of ground beef.
Refried beans = chocolate pudding
Lettuce = green fondant, grated w/a cheese grater. (Another way to get a lettuce effect is to dye coconut shavings green, but Adam doesn't like coconut, and it was his b-day cake, so we had to go a different route.)
Mozzarella & cheddar cheese = basic frosting (powdered sugar + butter), w/food coloring
Onions = white gum drops, cut into eighths
Tomatoes = candy Dots, cut in half
The freakishly realistic black olives = These were our money shot. People kept asking if we'd used actual black olives. They were Dots, cut crosswise, with center holes poked out with a chopstick.
Sour cream/guac sides = Cool Whip, food coloring
Salsa side = Jello, orange & red, mixed up together to make it look chunky, with some of the leftover onions

The end result = the cake was basically inedible. We'd inadvertently bought the spice-flavored gum drops and the white ones (the onions) tasted like wintergreen. These are fine on their own, but they clashed with the other cake ingredients and the end result was a weird, chemical wintergreen. I went through and picked out the onions but it was pointless, because they'd each left this invisible little puddle of chemical wintergreen flavor. Oh well. They looked just great as onions, though—they really did.

Agreed. Thank you, Marti.