Preheat oven to 325°F / 163°C.
Spray a loaf pan with nonstick cooking spray.
In a large mixing bowl, whisk together melted butter, mashed banana, and brown sugar until evenly combined (it will be slightly lumpy). Whisk in eggs and vanilla.
In a second bowl, whisk together flour, peanut butter powder, baking soda, and salt.
Pour dry ingredients over wet and stir just until no dry spots remain.
Stir chocolate chips into batter.
Pour batter into prepared loaf pan. Spoon peanut butter over the top of the batter. Using a knife, draw swirls through the peanut butter so that it blends into the batter. Scatter a few chocolate chips on top.
Bake bread until the center is set, 60 to 70 minutes.
Allow to cool before slicing and serving.