Heat oven to 350.Grease two 8 inch cake pans and one 2 1/2 to 3-qt metal or ovenproof glass mixing bowl with a rounded bottom.
Prepare 1 double batch cake batter as directed on package using 2 packages cake mix.Then prepare 1 single batch.Fill each layer-cake pan 2/3 full. Scrape remaining batter into prepared bowl.Bake pans 30 to 35 minutes and bowl 55 to 60 minutes or until a pick inserted in center of cakes comes out clean.Cool on wire racks,15 minutes for pans and 30 minutes for bowl.Invert cakes on racks and let cool completely.
TOMATO SLICES:Place plain cookies on wire rack set over waxed paper.Put 1/2 cup vanilla frosting in a small saucepan.Stir over low heat until melted and smooth.Remove from heat and stir in red food color and a little bit of yellow if needed until frosting is tomato-colored.Brush or spoon on top and sides of cookies.Let stand at least 30 minutes,until firm to touch.
EYES:Use a dot of vanilla frosting to glue M&M's pupils on marshmallows.
LETTUCE: Use some vanilla frosting and color it green with food color.Use pastry bag and squiggle green around to make it look like lettuce.
Put remaining vanilla frosting in a medium bowl.Stir in milk-chocolate frosting and red and yellow food color a little at a time til frosting is the color of a hamburger bun.
TO ASSEMBLE: Place 1 cake layer on serving plate.Cover with bun colored frosting.Place remaining cake layer on waxed paper.Cover with chocolate fudge frosting.Press crushed snap cookies into frosting to simulate a hamburger patty.Using pancake turners lift patty onto bun.Spoon mustard about 1-in. from edge of top of burger letting some run down sides.Top with tomato slices.
Trim hump off bowl cake.Place cake trimmed side down on wax paper and frost with remaining bun-colored frosting.Lift onto tomato-topped burger.Glue eyes in position with frosting.Press pignoli nuts in place.