Preheat your oven to 350°F (175°C). Grease a 9×5-inch loaf pan with butter or cooking spray, then line with parchment paper for easy removal.
In a large bowl, mash the ripe bananas with a fork until smooth with just a few small chunks remaining.
Add the melted butter, sugar, eggs, and vanilla to the mashed bananas. Whisk until well combined and smooth.
In a separate bowl, whisk together the flour, baking soda, salt, and cinnamon (if using).
Gently fold the dry ingredients into the wet mixture using a rubber spatula. Mix only until just combined—avoid overmixing.
Fold in most of the chocolate chips, reserving a small handful for topping.
Pour the batter into your prepared loaf pan and sprinkle the reserved chocolate chips on top.
Bake in the preheated oven for 55-60 minutes, or until a toothpick inserted into the center comes out clean with a few moist crumbs (but no wet batter).
Let the bread cool in the pan for 15 minutes before transferring to a wire rack to cool completely.