Place some coconut in a plastic bag and add two drops green liquid food coloring.
Mix the coconut and the food coloring in the bag with your fingers until coconut is convincingly green.
Place a vanilla wafer flat side up. Apply yellow decorating icing across vanilla wafer, taking care to get some at the edge so that it will clearly show later.
Apply red frosting across cookie, taking the same care you did with the yellow.
Add coconut to cookie, ensuring that some hangs slightly over the edge.
Place one thin chocolate cookie on top of frosting, forming a fake hamburger patty.
Add red frosting to the top of the chocolate cookie.
Place another vanilla wafer on top of the chocolate cookie. Set aside and repeat until desired number of Hamburger Cookies are ready.
Gently spread water across top of completed cookies. Do not apply too much water, as that can make cookies soggy.
Place sesame seeds on top cookie where water was spread. A light tap should get them to stick.
Serve and enjoy!