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 use a wooden spoon or spatula!) Stir in vanilla, lemon juice, and eggs. Stir until smooth, then stir in flour mixture. Mixture may be slightly lumpy because of the ground oats. Stir in chocolate chips and walnuts.

Line a cookie sheet with wax or parchment paper or a silicone baking mat. Scoop 1/4 cupfuls of the dough into balls and place on the cookie sheet. You do not need to space them; this is just for chilling. Cover well with plastic wrap and chill at least 4 hours or overnight before baking.

Preheat oven to 350°F. Place cookies well spaced on cookie sheets lined with parchment paper or silicone baking mats. Slightly depress each ball with the palm of your hand.

Bake for 13-17 minutes. Do not over bake - these are best a bit under done.