Preheat oven to 350 degrees F and spray a 9 x 13 inch baking pan with nonstick spray.
In a large bowl whisk together the eggs, milk, melted butter, maple syrup, brown sugar and vanilla extract until combined. Stir in the oats, baking powder and cinnamon until all of the ingredients are combined.
Let the oatmeal batter sit for 10 minutes to absorb all of the ingredients. Spread the oatmeal batter evenly into the greased baking pan and bake for 20-25 minutes or until the top looks golden brown.
While the oatmeal is baking you can make the icing. Simply whisk together the powdered sugar and milk in a small bowl until icing has formed. If the icing seems too thick, add more milk. If it's too thin, add more powdered sugar.
Once the oatmal is baked let cool for 10 minutes and slice into squares. Drizzle with icing and serve immediately. It is best when served fresh and warm, enjoy!