Preheat oven to 350°F (175°C) and line baking sheets with parchment paper.

Cream together softened butter and granulated sugar in a large bowl until light and fluffy.

Beat in the egg and vanilla extract until well combined.

Stir in the mashed bananas until evenly distributed.

In a separate bowl, whisk together flour, baking soda, salt, and ground cinnamon.

Gradually incorporate the dry ingredients into the wet ingredients until just combined.

Fold in the chopped walnuts.

Drop rounded tablespoons of dough onto the prepared baking sheets, spaced 2 inches apart.

Bake for 10-12 minutes or until the edges are lightly golden and the centers are set.

Cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.