Preheat oven to 350 F. In a large bowl, whisk together flour, sugar, salt, baking soda, and baking powder. Add in milk, oil, eggs, and vanilla extract. Whisk until smooth.
Pour cake batter into a greased baking dish. Bake for 30-35 minutes. Let cool completely.
For the frosting, beat softened butter with powdered sugar, vanilla extract, and milk. Beat until smooth. Add in green food coloring and mix until fully green.
Evenly spread frosting over the cake. Use the decorating icing to decorate the hair and mouth. Place two oreo cookies at the top for the eyes.
