Preheat your oven to 350°F (175°C).
Line two baking sheets with parchment paper.
In a medium bowl, whisk together the flour, baking soda, salt, and cinnamon. Set aside.
In a large bowl, cream together the butter, brown sugar, and granulated sugar until light and fluffy, about 2-3 minutes.
Beat in the egg and vanilla extract until well combined.
Gradually add the dry mixture to the wet mixture, mixing until just combined.
Fold in the oats, walnuts, and chocolate chips until evenly distributed.
Scoop rounded balls of dough onto the prepared baking sheets, leaving space between each cookie.
Bake for 10-12 minutes, or until the edges are golden brown.
Let cookies cool on the sheets for 5 minutes before transferring to a wire rack.
