For cake: Bring water to a boil in a small saucepan. Add the oats and butter and let sit for 10 minutes.
Preheat oven to 350 degrees.
Pour oat mixture into a large mixing bowl. Beat in the sugars and eggs till well combined.
Add the flour, baking soda, salt, cinnamon, and nutmeg and stir till well combined.
Pour into a well greased 9x13" pan and bake at 350° for 30-35 minutes.
For icing: Combine all ingredients in a small bowl, stir until well combined. Spread over hot cake and broil for 1-2 minutes or until bubbly. Watch carefully!