1. Place the egg whites in a container and whisk until firm peaks form.
2. Using a spatula, carefully combine the zest of one lemon, oat flour, and yeast. You can add your preferred sweetener.
3. Place the mixture in the oven at 180°C/350ºF for 15 minutes. Prick with a stick to determine if it's ready; if the stick comes out moist, let it sit for a few more minutes.
4. Allow it to rest at room temperature.