Slice banana lengthwise or diagonal if you're trying to impress someone with your culinary skills; width-wise if you're just trying to feed a hungry child; spread banana slices over peanut butter.
Plop the other slice of bread on top.
Squish lightly to compress the ingredients.
ALTERNATIVES: Honey or jam may be applied before adding the banana slices, although this would slightly alter the DNA perhaps resulting in a hybrid monkey, maybe even upgrading completely to a gorilla! Use with caution!