In a large mixing bowl, combine the mashed banana, vegetable oil or melted butter, and packed light brown sugar.
Mix until the ingredients are fully combined.
Add the egg yolk and vanilla extract.
Mix until the wet ingredients are smooth and evenly incorporated.
Add the all-purpose flour, baking soda, ground cinnamon, and salt.
Stir until the dough is fully combined and no visible streaks of flour remain.
Fold in the chocolate chips until evenly distributed throughout the dough.
Cover the bowl and allow the dough to rest at room temperature for approximately 15 minutes while the oven preheats. This allows the flour to hydrate and improves the cookie texture.
Line a cookie sheet with parchment paper.
Preheat the oven to 350°F.
Once the oven is preheated, use a 1-ounce cookie scoop or spoon to portion the dough onto the prepared cookie sheet.
Place the dough balls approximately 2 inches apart to allow room for spreading.
Bake for 10 to 11 minutes, or until the edges are set and the cookies have puffed up. The centers should still appear slightly underbaked.
Remove the cookie sheet from the oven.
Allow the cookies to cool on the baking sheet until they are firm enough to handle.
Transfer the cookies to a wire rack and allow them to cool completely before serving.