Preheat oven to 350°F (175°C). Line two large baking sheets with parchment paper.

In a medium bowl, whisk together the all-purpose flour, baking soda, ground cinnamon, and salt. Set aside.

In a large bowl using a handheld or stand mixer, beat the softened butter, granulated sugar, and light brown sugar together on medium speed until light and fluffy, about 2-3 minutes.

Add the mashed banana, egg, and vanilla extract. Beat on medium speed until well combined. The mixture may look slightly curdled, which is normal.

Reduce the mixer speed to low and gradually add the dry ingredient mixture, mixing just until combined. Do not overmix.

Using a rubber spatula, fold in the semi-sweet chocolate chips.

For best results and to prevent spreading, cover the dough and chill in the refrigerator for at least 30 minutes.

Drop rounded tablespoons of dough (about 1.5 tablespoons each) onto the prepared baking sheets, spacing them about 2 inches apart.

Bake for 11-14 minutes, or until the edges are golden brown and the centers are set. The cookies will look soft in the middle.

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