Preheat oven to 350 degrees. Spray a 9 by 9-inch baking dish with non-stick cooking spray (a 7 by 11-inch dish would work as well).
Add oats to a medium mixing bowl the pour boiling water over oats, let rest until cool.
Meanwhile in a large mixing bowl using an electric hand mixer (or use electric stand mixer), whip together butter, brown sugar and granulated sugar until pale and fluffy.
Mix in eggs, vanilla, cinnamon and nutmeg then mix in cooled oat mixture.
Sprinkle baking soda and salt across top then pour in flour and mix until combined.
Pour into prepared baking dish, bake in preheated oven until just cooked through, about 30 minutes.
Meanwhile in a medium mixing bowl stir together melted butter, milk, vanilla, brown sugar, coconut, and pecans.
Remove cake from oven once cooked through and pour and spread mixture evenly over top.
Preheat oven to broil then return cake to oven (in center) and broil until mixture is bubbly and coconut is just starting to toast on ends, about 1 - 2 minutes (don't walk away from it while broiling!).
Let cool on a wire rack for at least 20 minutes then cut into slices and serve.
Recipe source: inspired by Allrecipes