Preheat the oven to 350 degrees F. Prepare the cookie mix as the label directs for drop cookies, mixing in the cornmeal. Roll out into a 13-inch round on floured parchment paper; trim into a 12-inch circle with a paring knife.
Cut the cookie in half with the paring knife to make 2 semicircles, then use kitchen shears to cut through the parchment so each semicircle is on its own piece of parchment.
Slide 1 semicircle (on the parchment) onto a rimmed baking sheet. Press the straight edge of the semicircle up against the rim as shown. Slide the other semicircle flat onto a separate baking sheet. Bake until golden, 12 minutes.
Remove the cookies from the oven. Use the handle of a wooden spoon to shape the edge of the curved cookie. Let the cookies cool completely on the baking sheets.
Put the curved cookie on a clean parchment-lined baking sheet. Cut the ice cream out of the carton; slide onto the cookie. Use plastic wrap to gently press the ice cream so that it goes almost to the edge.
Sprinkle the side of the ice cream with the cereal, pressing to adhere. Transfer to the freezer.
To make "lettuce," combine the coconut with 3 drops green food coloring, 1 drop yellow food coloring and a small splash of water in a resealable plastic bag; shake and massage until the coconut is light green.
Slice the Circus Peanuts into thin strips to look like shredded cheese; chop the cherries for the tomatoes.
Sprinkle the coconut, Circus Peanuts and cherries over the cereal. Place the other cookie on top of the ice cream so the two cookie edges line up. Freeze until firm, at least 2 hours.
Photograph by Ralph Smith
Recipe courtesy of Food Network Magazine