Preheat oven to 375 degrees. Line baking sheets with parchment paper. Place the butter in a large bowl and cream lightly with an electric mixer. Add the sugars and beat on medium speed for about 2 minutes.
Add the eggs, one at a time, beating well after each addition. Add the vanilla and lemon juice and mix well. In a separate bowl, stir together the flour, oatmeal, baking soda, salt and cinnamon.
Add to the creamed butter mixture and stir well to blend. Add chocolate chips and walnuts and stir to combine. Using a 1/4 cup measure or a 2-oz ice cream scoop, drop the batter on the parchment-lined pans, leaving 2 -3 inches between each cookie.
Bake for 13 - 15 minutes or until lightly browned around the edges. Remove from parchment and cool on wire racks. Yield: approximately 4 dozen