Powdered sugaroptional, will help make the frosting a little less sticky
In a medium-sized bowl, mash your banana very well with a fork until it’s an almost liquid state. Add in your peanut butter and mix very well. Add powdered sugar, 1 tablespoon at a time, until you reach desire consistency and sweetness. I must have added about 2tbsp. If you want to avoid sugar, you could omit completely, you’ll simply end up with a stickier and of course less sweet icing.
Once your frosting/icing is ready, simply pour it over your cake and spread evenly.