Cream butter, sugar and brown sugar in a mixing bowl using a stand or hand mixer on medium speed for about 2 minutes.
Add egg, vanilla, and lemon juice. Use the mixer and blend on low for 30 seconds. And then blend on medium for a couple of 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.
Fold in chocolate chips and walnuts.
Line the air fryer basket with air fryer parchment paper. Scoop the cookie dough into balls (about 2 tablespoons) and place them in the basket about 1 1/2 to 2 inches apart. Use wet hands and flatten the top of the cookies. The batter is really sticky. Wet hands work well while handling it.
Air fry for 6-8 minutes on 300 degrees.
Remove the air fryer basket and allow the cookies to cool for 5 minutes before removing them from the basket. If you handle them too soon they will not firm up and will crumble.
Transfer the cookies to a wire rack to cool for an additional 10 minutes.
Sprinkle with sea salt if you wish.