Combine sugars and softened butter in the bowl of a stand mixer. Mix on medium speed until creamy.
Add eggs, vanilla, and lemon juice and mix on low for 30 seconds, then increase speed to medium and mix for 2 minutes more, until light and fluffy, scraping the bowl.
Decrease mixer speed to low. Add flour, oats, baking soda, salt, and cinnamon. Mix for 45 seconds. Do not over mix.
Remove bowl from the mixer. Stir in chocolate chips and walnuts.
Preheat oven to 300 F. Line two large baking sheets with parchment paper.
Portion dough with a scoop (about 3 tablespoons) onto the baking sheet about 2 inches apart.
Bake for 20-23 minutes or until edges are golden and the center is soft. Remove from oven and cool for 1 hour.
