Preheat an oven to 350°F (175°C).
Spray a muffin tin with cooking spray.
Separate the egg whites and beat them until soft peaks form. Set aside.
In a bowl, combine together the egg yolks, spinach, and oats. Season with salt and pepper. Mix in the egg whites.
Pour the mixture into a muffin tin. Bake for 15-17 minutes. When done, allow the muffins to cool completely before taking them out. Enjoy!