• Preheat the oven to 350 degrees Fahrenheit. Spray a 9 x 13 x 2-inch baking pan with nonstick cooking spray, and set aside.
• Add 1 cup rolled oats and 1 ¼ cup boiling water to a medium bowl and let it stand while the rest of the batter is prepared.
• Add ½ cup softened unsalted butter, ½ cup granulated sugar, and ½ cup packed light brown sugar to a large bowl and beat it on medium-high speed with a hand mixer or stand mixer fitted with the paddle attachment until light and fluffy. Add the 2 large eggs and mix until combined.
• Whisk together 1 ⅓ cup all-purpose flour, 1 teaspoon baking soda, ½ teaspoon salt, 1 teaspoon ground cinnamon, and ¼ teaspoon ground nutmeg in a medium bowl. Add the flour mixture to the butter mixture and mix until combined. Add 1 teaspoon vanilla extract and the soaked oats and mix until combined.
• Pour the batter into the prepared baking pan and bake for 30-40 minutes, until a toothpick comes out clean from the center of the cake.

Frosting

• While the cake is baking, prepare the frosting by stirring together ¼ cup melted salted butter, 3 tablespoons milk, 1 teaspoon vanilla extract, ½ cup packed light brown sugar, 1 cup sweetened shredded coconut, and ½ cup chopped pecans. Once the cake has finished baking, spread the frosting over the hot cake.
• Switch the oven to the broiler on high and broil the frosted cake for 1-2 minutes, just until the edges of the coconut start to toast. This happens quickly, so keep a close eye on it.
• Let the cake cool for at least 20-30 minutes before slicing and serving.