Prep: Preheat oven to 350°F (175°C). Cover 2 baking sheets with parchment paper.
Grind Oats: Place rolled oats in a blender or food processor and process until finely ground.
Dry Mix: In a mixing bowl, combine the ground oats, flour, baking soda, salt, and cinnamon.
Wet Mix: In another large bowl, cream butter, brown sugar, granulated sugar, vanilla, and lemon juice together using an electric mixer. Add eggs and beat until fluffy.
Combine: Stir the flour mixture into the egg mixture, blending well.
Add-Ins: Add the 3 cups of chocolate chips and walnuts (if using) to the dough and mix well.
Scoop: Using a 1/4 cup measure or large scoop, form round balls with the dough and place them 2 1/2 inches apart on prepared baking sheets.
Bake: Bake until cookies are lightly browned, 16-18 minutes.
Cool: Transfer to a wire rack to cool completely.
Drizzle (Optional): Melt extra chocolate chips in a small bag, snip the corner, and drizzle over cooled cookies.