Preheat the oven to 350 F.
Break up the banana in pieces in your food process or blender. Add all the remaining ingredients except the peanut butter chips or chocolate chips (which are for sprinkling), and blend until smooth and thick.
Pour the batter into a small baking dish. You can line it with parchment paper if you'd like, or just spray with non-stick cooking spray.
Bake for at least 10 minutes, but I usually need more like 15 and sometimes even 20 depending on how thick I make them. Start checking at 10, you want the top puffy and not wet to the touch, but for them to still have a bit of jiggle.
Let the brownies sit and cool for 5-10 minutes before digging, so they set a bit.