Preheat the oven to 350℉. Line a baking sheet with parchment paper then set it aside.
In a large mixing bowl, combine the oat flour, tapioca starch, sugar, baking soda, and salt. Mix well.
To the same mixing bowl, add the oil, lemon juice, vanilla, and lemon zest. Mix until a uniform cookie batter forms.
Take 12 rounded tablespoon portions of the dough and place them on the prepared baking sheet at least one-inch apart.
Bake for 12 minutes, or until the cookies are mostly firm.
While the cookies are baking, combine the powdered sugar and lemon juice in a small bowl and mix until you have a smooth white glaze.
Allow the cookies to set and cool for at least 5 minutes before glazing.
Once the cookies have cooled and firmed up, drizzle the glaze in a zig-zag pattern over the cookies, followed by an optional sprinkle of additional lemon zest. The glaze should set nearly immediately.
Enjoy!
Video
Notes
Storing and Freezing
Stored in an airtight container at room temperature, these cookies will last up to a week. In the refrigerator, they can last up to two weeks. You can freeze the baked cookies for up to 3 months. Thaw at room temperature or gently reheat in the oven for a few minutes.