Slice bananas into coins, add to bowl, and whisk in until fairly smooth.
Stir in walnuts.
Grease an 11x7 glass pan and pour in batter.
Drizzle on peanut butter, then swirl with a butter knife.
(Note: If you aren't using the goopier natural peanut butter you'll need to warm it in the microwave for 15-20 seconds to liquify a bit before pouring on brownies.)
Scatter chocolate chips on top.
Bake at 350 degrees for 45 minutes, or until a knife inserted in the center pulls out clean.