Preheat the oven to 350 degrees F (175 degrees C). Spray an 8-count mini loaf pan with cooking spray.
Mix sugar, applesauce, egg, and vanilla in a large bowl with a wooden spoon. Add in bananas, walnuts, and chocolate chips and stir to combine. Add flour, baking soda, cinnamon, and salt and stir until completely mixed. Spoon batter into the prepared loaf pan.
Bake in the preheated oven until a toothpick or fork inserted into the center comes out clean, 25 to 30 minutes. Allow to cool for at least 30 minutes.