Preheat your oven to 350 degrees Fahrenheit and line a baking sheet with parchment paper. Set it aside while you prepare the dough. In a mixing bowl, whisk together the flour, baking soda, and salt. Set this dry mixture aside.

In a large bowl using a hand mixer, cream the softened butter until smooth. Add the white granulated sugar and mix until the two are well combined.

Add the fresh lemon juice and lemon zest to the butter mixture and mix until fully incorporated. This is where all that bright citrus flavor gets built into the base of the cookie.

Alternately add the old-fashioned oats and the flour mixture to the bowl, mixing well between each addition until a soft dough forms.

Bake for 10 to 12 minutes, or until the cookies are golden brown around the edges. Let them cool on the baking sheet for 5 minutes before transferring to a cooling rack. Once cookies are completely cool, whisk together the powdered sugar and lemon juice until smooth. Drizzle or spread over the cooled cookies and allow the icing to set before serving.