Cream the butter, sugar, and brown sugar together in a stand mixed at medium speed for 2 minutes.
Add the eggs, vanilla, and lemon juice to the butter. Mix on low until just combined, then increase speed to medium and blend for 2 minutes. Scrape down edges of the bowl as needed.
Put the mixer speed on low and add the flour, oats, baking soda, salt, and cinnamon. Blend until just barely combined, about 45 seconds. Do not over mix.
Remove the bowl from the mixer. Add the chocolate chips and walnuts, and stir until just combined.
Preheat oven to 300F.
Scoop the dough into 3 Tablespoon sized balls. Place them about 2 inches apart on a parchment or silicone mat lined baking sheet.
Bake until the cookie edges are just starting to brown and the center is still soft, approximately 20 minutes.
Remove the cookies from the oven and let them cool on the baking sheet at least 20 minutes before removing them.
Notes
I found that letting the cookies cool on the baking sheet at least 20 minutes was important for them to not rip apart.You can make the cookies smaller and cook for a shorter time.It is important to let the eggs be at room temperature (not cold) so that when they are added to the butter, the butter does not clump up from the cold.Dough can be frozen in the ball shape and immediately baked, without thawing, with the same instructions.I normally refrigerate my cookie dough so that they do not spread too much. I found that with this recipe, there was no difference in spreading if they were chilled or not chilled. The only difference I found was that slightly chilled dough resulted in cookies that were more perfectly round. If you choose to refrigerate, 20-30 minutes is enough time.