Preheat your oven to 350°F (175°C).

In a large mixing bowl, cream together the softened butter, brown sugar, and granulated sugar until light and fluffy.

Add the egg, mashed bananas, and vanilla extract to the bowl. Mix until well combined.

In a separate bowl, whisk together the all-purpose flour, baking soda, and salt. Gradually add this dry mixture to the banana mixture, stirring gently until just combined.

Fold in the chopped walnuts and chocolate chunks using a spatula.

Using a cookie scoop or tablespoon, drop rounded balls of dough onto a baking sheet lined with parchment paper, leaving space between each cookie.

Bake for 10-12 minutes, until the edges are lightly golden and the centers remain soft.

Remove from the oven and let cool on the baking sheet for a few minutes before transferring to a wire rack to cool completely.