Preheat oven to 350º F with oven rack on center position.Grease the inside of a 9" x 5" loaf pan. Optional extra step: Add a strip of parchment paper for easier release. Cut 6 slices off one banana and set aside for garnish (if using).
Using a fork, mash the remaining bananas on a plate until mostly smooth.
Cream vegan butter, peanut butter, and sugar with hand beaters on high until light. (You could beat by hand with a wooden spoon or use a stand mixer as well.)
Add aquafaba (egg replacer), vanilla extract, and 2 tablespoons non-dairy milk. Beat on high until light and fluffy.
Measure out flour using a kitchen scale or the spoon and level method*. Whisk the baking powder and baking soda into the flour. Add the mashed bananas and flour alternately to the creamed ingredients mixing on low with the electric beaters or use a wooden spoon to stir just until incorporated without over mixing the batter. Optional: Add another tablespoon of almond milk if the batter is too thick.
Fold chocolate chips and/or chopped walnuts into the batter (if using).
Scrape the batter into the prepared loaf pan.
Garnish with banana slices, chopped walnuts, and chocolate chips if using.
Bake the banana bread at 350º F until golden and a toothpick inserted into the middle of the loaf comes out clean (~50-60 minutes).
Loosely cover the banana bread with a tin foil tent for the last 20 minutes if the crust is browning too quickly.
Let cool ~10 minutes in the loaf pan before releasing and transferring the banana bread to a wire rack to finishing cooling before slicing.