Pre-heat oven to 300°F.
In the bowl of a stand mixer, on medium speed, cream the butter, sugar and brown sugar for about 2 minutes.
Add eggs, vanilla and lemon juice, blending with mixer on low speed for 30 seconds, then medium speed for about 2 minutes, or until light and fluffy, scraping down bowl.
With mixer on low speed, add flour, oats, baking soda, salt and cinnamon, blending for about 45 seconds; don't overmix.
Remove bowl from mixer and stir in chocolate chips and walnuts.
Portion dough, with a 3-tablespoon scoop, onto a baking sheet lined with parchment paper about 2 inches apart.
Bake for 20 to 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.