Preheat oven to 350 degrees. Line a 9x13 inch baking dish with foil or parchment paper and spray with non stick cooking spray. Set aside.
In a large bowl whisk together the flour, cocoa powder, cinnamon, and sugar. Add in the melted butter, eggs, and vanilla extract and stir for 1-2 minutes just until combined. Fold in the chocolate chips if using.
Spread the batter into the prepared pan. Bake in preheated oven for 25-30 minutes.