Place oats in a small food processor or blender and grind until they turn powdery.
Place them in a medium sized bowl and whisk in the flour, baking soda, salt, and cinnamon. Set aside.
Stir together melted butter, brown sugar, and granulated sugar until smooth (no mixer needed, just a wooden spoon or spatula!).
Stir in vanilla, lemon juice, and eggs until smooth, then stir in the flour mixture.
Stir in chocolate chips and walnuts.
Line a cookie sheet with parchment paper or a silicone baking mat.
Scoop the dough into ¼-cup portions and roll into balls. Place them on a cookie sheet; there’s no need to space them apart since this is just for chilling.
Cover well with plastic wrap and chill for at least 4 hours or overnight before baking.
Preheat oven to 350°F.
Place the cookies well-spaced apart on a cookie sheet lined with parchment paper or a silicone baking mat. Slightly flatten each ball with the palm of your hand.
Bake for 13-17 minutes. Be careful not to overbake; these cookies are best when slightly underdone. Enjoy!
