01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - In a large bowl, cream together the softened butter, brown sugar, and granulated sugar until light and fluffy.
03 - Add the mashed bananas, egg, and vanilla extract to the creamed mixture. Mix until well combined.
04 - In a separate bowl, whisk together the all-purpose flour, baking soda, ground cinnamon, and salt.
05 - Gradually add the dry ingredient mixture to the wet ingredients, stirring until just combined. Fold in the rolled oats and chocolate chips or walnuts if using.
06 - Drop tablespoon-sized mounds of dough onto the prepared baking sheets, spacing about 2 inches apart. Bake for 10–12 minutes until edges are golden and centers appear just set.
07 - Let the cookies rest on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.