Gather all ingredients together. You can use gluten-free flour and gluten-free oats, or you can use regular. Whichever you prefer. Xanthan gum is for a better binding purposes, it's optional.
Mix dry ingredients together. It is better to use wide bowl insteal of a measuring bowl. It will be easier to mix. I actually transfered later into a bigger bowl.
Add wet ingredients (egg whites & water) to dry, and combine well to achieve batter/dough. Make sure all incorporated evenly and no dry ingredients at the bottom.
Get loaf pan, sprinkle a bit of flour at the bottom (optional). Pack dough into the loaf pan in a desired form. Add little bit oats on top for decoration (optional).
Bake for 45 minutes at 365 F. To make sure it's fully baked, stick a tooth pick or a knife in the middle and see if it comes out clean. If yes - done, if not - bake 5-10 min more until done.
Let it cool, slice and serve.