Set oven to 350°F (177°C). Prepare your loaf pan by greasing or lining with parchment paper.
In a large bowl, thoroughly mash the bananas.
Add the egg, melted butter, milk, avocado oil, brown sugar, and vanilla extract to the mashed bananas and mix until well combined.
In a separate medium bowl, whisk together the flour, baking powder, and salt.
Gradually add the dry ingredients to the wet, stirring until just combined to avoid overmixing.
Fold in the sourdough discard.
Gently fold in the chocolate chips.
Pour the batter into the prepared loaf pan. Bake for 50-60 minutes, or until a toothpick inserted into the center comes out clean. Depending on your oven, you may want to start checking it around the 40 minute mark.
Allow to cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.