Preheat the oven or air fryer to 350F and prepare a baking sheet with parchment.
In a bowl, mash the bananas until completely smooth. Stir in the vanilla.
Add the flour and baking powder and softly stir until a batter is formed. Now, oil your hands, and transfer the dough to a cutting board. Softly knead (the dough will be slightly sticky) until you are able to achieve a slightly firm dough ball.
Then, with your hands, separate into 9 to 12 golf sized balls, rolling to be as round as possible. Spray with oil.
Place on the baking sheet and bake for 6 to 8 minutes, until browned on the outside and puffed up. In the meantime, stir together the sugar and cinnamon in a bowl until combined.
Take the donut holes, and toss them in the cinnamon and sugar until coated. Enjoy immediately, or store in the fridge for up to 4 days.