Preheat oven to 350. Spray a 9/13 pan with nonstick cooking spray.
Stir together the ingredients.
Spread in the prepared pan.
Bake for 20 minutes, until the center only jiggles slightly.
Add peanut butter as a topping, if desired. Cool completely.
Topping (optional)
Drop tiny spoonfuls of peanut butter on the hot brownies. It will melt slightly.
Place slices of banana on the brownies after they are cooled.
Notes
Brownie Mix: Choose one that includes chocolate chips or chunks for the best results.For brownie mixes larger than 15 ounces, such as Ghiradelli which is 20 ounces, increase both the banana and peanut butter by a couple of tablespoons. You should try to match the consistency in my photos.