Preheat oven to 350°F and grease a 9×13 cake pan with nonstick spray, set aside.
In a bowl combine oats with boiling water. Let soak for 15 minutes.
In another bowl whisk together flour, cinnamon, baking soda, salt, and nutmeg.
In a large mixing bowl beat granulated sugar, brown sugar, and butter on a medium speed until light and fluffy, about 4 to 5 minutes, scrape the sides and bottom of the bowl as needed.
Beat in eggs, one at a time, until well incorporated. Beat in the vanilla.
Gradually add the dry ingredients until well combined. Add in oat mixture, beating until well combined.
Spread evenly into the prepared baking pan and bake for 25 to 30 minutes, a toothpick inserted should come out with a few moist, not wet crumbs.
To make the topping:
Remove cake from the oven and change the oven’s setting to broil.
In a medium bowl, whisk butter, light brown sugar, milk, and vanilla. Stir in coconut and chopped nuts.
Spread mixture over warm cake.
Place under the broiler until the edges of coconut start to brown, about 1 to 2 minutes.
Cool cake for a minimum of 30 minutes before serving.
