Step 1Heat the oven to 350 degrees. Grease a 13x9-inch baking pan.
Step 2Bring the water to a boil in a saucepan. Add the oatmeal, reduce the heat and cook until the water is absorbed, about 5 minutes. Remove the oatmeal from the heat and set aside. Allow it to cool to room temperature.
Step 3Cream the butter in a large mixing bowl and gradually beat in the granulated and brown sugars. Blend in the eggs and vanilla and beat for 2 minutes. Add the oatmeal.
Step 4Mix the flour, baking soda, salt, cinnamon and nutmeg in a separate bowl. Gradually add the dry ingredients to the sugar-butter mixture and blend in. Mix for 2 minutes.
Step 5Pour the batter in the pan. Bake the cake until a toothpick inserted in the center comes out clean, about 45 minutes. Allow the cake to cool before frosting.
Step 1Combine the butter, sugar, cream, nuts and coconut and spread over the cooled cake.