Preheat oven and pan:

Heat oven to 350°F (175°C). Grease a mini loaf pan or line with paper liners.

Mix wet ingredients:

In a large mixing bowl, use a fork to thoroughly mash the bananas with the melted butter until smooth. Stir in the sugar until well blended. Add the egg and beat until incorporated, then mix in the vanilla.

Fold dry ingredients and chips:

Evenly distribute the baking soda, salt, flour, and cinnamon over the banana mixture. Fold in three additions until the batter is smooth and creamy. Fold in the chocolate chips until evenly dispersed.

Bake and cool loaves:

Bake for 25 to 35 minutes, until a toothpick inserted in the center comes out clean. Let cool in the pan for 5 minutes, then run a knife around the edges to loosen. Remove loaves from the pan and place on a wire rack to cool completely, about 2 hours. For storage, wrap tightly in plastic wrap or refrigerate for up to 10 days.