Preheat your oven to 350°F (175°C).

Prepare a 9x9-inch baking pan by greasing it or lining it with parchment paper.

In a large mixing bowl, combine the mashed bananas, granulated sugar, brown sugar, and melted butter. Mix until well combined. Add the egg and vanilla extract, stirring until smooth.

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

Fold in the semi-sweet chocolate chips until evenly distributed.

Pour the batter into the prepared baking pan and spread it evenly. Bake for 25-30 minutes, checking for doneness with a toothpick.

Let the bars cool in the pan for about 10 minutes before transferring to a wire rack to cool completely. Cut into squares and serve.