1) In a medium bowl, mash together banana and peanut butter with a fork until mixed.
2) Add in Greek yogurt and use a hand mixer to beat until smooth. Then add in powdered sugar (1 cup for sweeter version) and beat until smooth a second time.
3) Dip pretzels in the dip. You can freeze the dipped pretzels but you have to keep them cold or they will melt. Personally, I just like to serve it as a dip and let people dip their own pretzels!