In a large bowl, mix together the melted butter (or vegetable oil), packed brown sugar, and mashed banana until everything is well incorporated and smooth.

Next, incorporate the egg yolk and vanilla extract into the mixture, stirring until fully combined and creamy.

Gradually add the all-purpose flour, salt, baking soda, and ground cinnamon to the bowl, stirring gently until no dry flour remains.

Gently fold in the chocolate chips, ensuring they’re evenly distributed throughout the dough. Cover the bowl with a clean cloth or plastic wrap, allowing it to rest for about 15 minutes.

Meanwhile, preheat your oven to 350°F (175°C) and prepare a baking sheet by lining it with parchment paper.

Use a tablespoon to scoop portions of dough and place them onto the prepared cookie sheet, spacing them about 2 inches apart.

Place the cookie sheet in the preheated oven and bake for 10 to 11 minutes, until the edges are set and the centers look slightly underbaked.

Once baked, take the cookies out and let them cool on the baking sheet for a few minutes before transferring to a wire rack.