Add cupcake liners to a muffin pan and divide the batter between 12 cupcakes. Bake the cupcakes for 20-23 minutes, then remove and allow to cool completely.
While the cupcakes cool, make the frosting by beating the butter, cocoa powder, powdered sugar, and milk. Whip until light and fluffy. Add to a piping bag.
Pour a tablespoon of water and two drops of green food coloring to a container with a lid, like a mason jar. Add the coconut and shake until the coconut is all green.