Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a mixing bowl, beat together the softened butter and brown sugar until creamy.
Add in the mashed bananas, egg, and vanilla extract, mixing until well combined.
In a separate bowl, whisk together the all-purpose flour, baking soda, salt, and ground cinnamon.
Gradually add the dry ingredients to the banana mixture, stirring until just combined. Avoid over-mixing.
If desired, fold in the chocolate chips and/or nuts for added texture and flavor.
Using a spoon or cookie scoop, drop tablespoon-sized portions of dough onto the prepared baking sheet, spacing them about 2 inches apart.
Bake in the preheated oven for 10-12 minutes, or until the edges are lightly golden and the centers look set.
Remove from the oven and let the cookies cool on the baking sheet for 5 minutes. Then, transfer them to a cooling rack to cool completely.