Oat flour is a gluten-free form of whole grain flour made from whole oats that have been ground into a powder. Oat flour gives baked goods more flavour than regular all-purpose flour. It gives a chewier and crumblier texture.
Try reducing the flour (whether all-purpose flour or a gluten-free blend) by 25% and replacing it with an equal amount of oat flour. It enhances their irresistibly thick and chewy texture.