Preheat your oven to 350°F (175°C). Line a cookie tray with parchment paper or use a silicone baking mat.

In a medium bowl, mix the sugar, peanut butter, and baking powder until well combined.

In a separate small bowl, mash the banana until smooth. Stir it into the peanut butter mixture until fully incorporated.

Using a cookie scoop or tablespoon, form dough into balls. Roll each one in a small bowl of sugar until fully coated.

Place cookie balls on the baking sheet. Press each gently with the tines of a fork in a criss-cross pattern for that classic peanut butter cookie look.

Bake in the preheated oven for 10 minutes, or until edges are just turning golden brown. Let cookies cool on the tray for 5 minutes before transferring to a rack.