Make the lettuce: Mix the vodka and confectioners' sugar in a pie dish. Add a few drops each of green and yellow food coloring and mix gently with a pastry brush. Do not fully mix; you want to have a few shades of green in the dish.
Lay out the wafer paper on a piece of parchment lightly coated with cooking spray. Brush with the food coloring mixture to fully cover, painting darker shades of green in some spots. Let dry until crisp, at least 2 hours.
Coat a 1 1/2-quart ovenproof bowl and 3 muffin cups with cooking spray. Prepare the cake mix as directed; fill the muffin cups with batter, then pour the rest into the bowl. Bake at 325 degrees F, 15 minutes for the cupcakes and 45 to 50 minutes for the bowl cake. Let cool.
Make the croutons: Cut the cupcakes into 3/4-inch squares. Toast under the broiler until lightly browned; set aside.
Remove the bowl cake and cut in half horizontally with a long serrated knife. Spread frosting on the bottom half and cover with the top half.
Place the bowl cake in a salad bowl that's slightly larger than the cake. Frost the top of the cake. Reserve 1/2 cup frosting for the dressing.
Tear the green-tinted wafer paper into small pieces and arrange on top of the cake; reserve a few pieces for the dressing.
Shave the white chocolate into thin shards with a vegetable peeler. Sprinkle the white chocolate and cake croutons on top of the cake.
Melt the reserved frosting in the microwave until pourable. Crumble some reserved green wafer paper into the frosting to look like herbs; stir, then pour into a salad dressing bottle.