Preheat oven to 300 degrees. Line baking sheet with parchment paper; set aside.
In a stand mixer, cream the butter, sugar, & brown sugar on medium speed for 2 minutes. Add eggs, vanilla, lemon juice, & blend on low speed for 30 seconds before increasing to medium speed for 2 minutes, or until light & fluffy, scraping down the sides of the bowl. With mixer speed on low, add flour, oats, baking soda, salt, & cinnamon & blend for 45 seconds without over mixing. By hand, stir in the chocolate chips & walnuts.
Form 3 tablespoons dough balls & place 2 inches apart on prepared baking sheets. Bake for 20-23 minutes or until edges are golden brown & center is soft. Remove from oven & allow to cool 1 hour on baking rack before removing.