01 - Preheat the oven to 350°F. Line a baking sheet with parchment paper and set aside.
02 - In a large mixing bowl, beat the softened butter, brown sugar, and granulated sugar together using an electric mixer or whisk until the mixture is light and creamy, about 2 to 3 minutes.
03 - Add the mashed bananas, egg, and vanilla extract to the creamed mixture. Stir until all wet ingredients are thoroughly combined.
04 - In a separate bowl, whisk together the rolled oats, all-purpose flour, baking soda, ground cinnamon, and salt until evenly distributed.
05 - Gradually add the dry ingredient mixture to the wet ingredients, folding gently with a spatula until just combined. Avoid overmixing to keep the cookies tender.
06 - Gently fold in the chocolate chips or chopped walnuts, if using, until evenly dispersed throughout the dough.
07 - Drop tablespoon-sized mounds of dough onto the prepared baking sheet, spacing them approximately 2 inches apart to allow for spreading.
08 - Bake on the center rack for 10 to 12 minutes, or until the cookie edges are golden while the centers remain soft and slightly under-set.
09 - Allow the cookies to rest on the baking sheet for 5 minutes, then transfer them to a wire cooling rack to cool completely before serving.