In a large bowl, mash the overripe banana, then mix it with the vegetable oil (or melted butter) and the packed light brown sugar until well combined.

Add the egg yolk and vanilla extract to the bowl. Stir thoroughly until smooth and cohesive.

To that mixture, add the all-purpose flour, baking soda, ground cinnamon, and salt. Stir gently until all ingredients are just combined and there are no visible streaks of flour.

Fold in the chocolate chips, making sure they are evenly distributed throughout the dough.

Cover the bowl and let the dough rest for about 15 minutes while the oven preheats — this hydrates the flour and yields a softer texture. Broma Bakery

Line a baking sheet with parchment paper and preheat your oven to 350°F (177°C).

Using a cookie scoop or a spoon, scoop out dough balls about 1-inch in diameter, placing them roughly 2 inches apart on the prepared baking sheet. Be aware that the dough will be a little wet.

Bake the cookies for 10–11 minutes, or until the edges are set but the centers remain slightly undercooked and puffed.

Remove the cookies from the oven and allow them to cool on the baking sheet so they can finish setting into a perfectly soft and gooey texture.