In a large mixing bowl, combine 1/2 cup of melted butter (or vegetable oil), 1 cup of packed light brown sugar, and 1/4 cup of well-mashed overripe banana. Use a whisk to blend until smooth and creamy, about 1-2 minutes.

Mix in 1 egg yolk and 1 teaspoon of pure vanilla extract until fully combined; scrape down the sides of the bowl to ensure everything is well mixed.

In the same bowl, gently stir in 1 1/3 cups of all-purpose flour, 1/2 teaspoon of baking soda, 2 teaspoons of ground cinnamon, and 1/2 teaspoon of salt until no dry flour remains; be careful not to overmix.

Fold in 2/3 cup of chocolate chips into the dough, ensuring even distribution without overworking the mixture.

Let the dough rest in the bowl for about 15 minutes; preheat your oven to 350°F (175°C).

Line a cookie sheet with parchment paper to prevent sticking; ensure the paper is flat and covers the entire surface.

After resting, use a cookie scoop or tablespoon to portion about 1 ounce of cookie dough per cookie, spacing them about 2 inches apart on the prepared cookie sheet.

Bake in the preheated oven for 10-11 minutes; edges should be set and centers may appear slightly underbaked.

Remove from the oven and let cool on the cookie sheet for a few minutes before transferring to a wire rack to cool completely.