Preheat the oven to 350 and prepare a baking sheet with nonstick cooking spray.
Using a food processor, pulse the oats a few times. Be sure not to do it too much in order to avoid turning it to flour.
In a medium mixing bowl, combine the oats, flour, baking powder, baking soda, salt, cinnamon, and nutmeg. Set aside.
In a large bowl, mix together the butter and sugars until it's light and fluffy. Add in the eggs and mix until well combined. Slowly add in the dry mixture, mixing well until all of it is added and well combined.
Scoop two tablespoons of cookie dough, roll into a ball, and place on the cookie sheet until you've used all your dough. Be sure to place the dough two inches apart. Bake 10-12 minutes.
Allow the cookies to cool for about 5 minutes before removing from the cookie sheet - they will spread and flatten a little more after removed from the oven.
Once the cookies are cooled, prepare the icing by mixing the powdered sugar and two tablespoons of milk. Slowly add more milk until you reach the desired consistency.
Lightly dip each cookie face down into the icing to allow the icing to drip into the cracks of the cookies. Cool the cookies on a rack to allow the icing to set. Serve and enjoy!