Preheat oven to 350 degrees. Line baking sheets with parchment paper.
Cream together peanut butter, mashed banana, and brown sugar until smooth.
Add egg and vanilla. Mix to combine.
In small bowl, combine the flour, baking soda and salt.
Add flour, mix well.
Roll into 1 inch balls and place on prepared sheets.
Dip for in sugar and press down on each ball of dough in criss cross pattern
Bake for 8 minutes.
Sprinkle warm cookies with sea salt (optional). Move to wire rack to cool completely.