Preheat your oven to 350°F and line a baking sheet with parchment paper.
Mash the ripe banana in a medium bowl until smooth.
In a large mixing bowl, cream together butter, brown sugar, and granulated sugar until fluffy.
Beat in the egg and vanilla extract, then stir in the mashed banana.
In another bowl, whisk together flour, baking soda, salt, and cinnamon.
Gradually add the dry ingredients to the wet mixture and stir until just combined.
Fold in chocolate chips or walnuts if using.
Drop spoonfuls of dough onto the baking sheet and bake for 10–12 minutes until lightly golden.
Cool on a wire rack before enjoying.