Preheat your oven to 300,prep your cookie sheets with parchment paper .
In a large mixing bowl, cream together the butter and both sugars. They, and I, suggest using a stand mixer to do this. it will take a couple of minutes at medium speed to get to that desired creamy texture.
Turn the mixer speed down to low and add the eggs, vanilla, and lemon juice. Blend for thirty seconds then up the speed to medium and mix for a couple more minutes until it becomes light. You will most likely need to stop to scrape the bowl a couple of times while blending this mixture.
Bump the mixer speed down to low an add the flour, oats, baking soda, salt and cinnamon. Mix until just mixed, about 45 seconds. To be honest, I usually suggest mixing these dry ingredients in a small or medium mixing bowl and setting it aside just after preheating the oven. The ingredients will mix into the batter more evenly if you choose to mix them together before adding them to the mixer.
Now, manually fold or stir in the chocolate chips and chopped walnuts. Use a cookie scoop that is about three tablespoons in size to scoop the cookies on to your prepped cookie sheets. Bake for 18-23 minutes or until the the edges begin to brown (center will be soft). Allow the cookies to cool on the baking sheet for about an hour before serving.