In a bowl, mix butter, sugar and brown sugar. Using a mixer, put it on medium speed for 2 minutes.
Add eggs, vanilla and lemon juice. Blend with mixer on low speed for 30 secs, then medium speed for 2 minutes or until light and fluffy.
With mixer on low speed, add flour, oats, baking soda, salt and cinnamon. Blend for 45 seconds. Don't over-mix.
Remove bowl from mixer and stir in chocolate chips and walnuts.
Portion dough with a coop onto a baking sheet with parchment paper.
Preheat oven to 300F. Bake for 20-23 minutes or until edges are golden brown and center is still soft.
Remove from oven and cool on baking sheet for about 1 hour.