Cream butter, sugar and brown sugar in the bowl of a stand mixer at medium speed for about two minutes.
Add eggs, vanilla and lemon juice, blending with mixer on low speed for 30 seconds, then medium speed for about two 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 scoop (about 3 tablespoons) onto a baking sheet lined with parchment paper about two inches apart.
Preheat oven to 300 degrees. 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 one hour.
Cook's note: You can freeze the unbaked cookies. There is no need to thaw. Preheat oven to 300 degrees and place frozen cookies on parchment paper lined baking sheet about two inches apart. Bake until edges are golden brown and center is still soft.