Preheat the oven to 375 degrees F (190 degrees C). Coat a baking sheet with cooking spray.

Beat egg in a large bowl. Mix in peanut butter, oatmeal, banana, sugar, chocolate chips, and vanilla. Roll dough into 1-inch balls and place onto the prepared baking sheet. Press on each ball with a spoon to flatten slightly.

Bake in the preheated oven for 9 to 12 minutes; cookies will look slightly raw. Cool for 10 minutes before serving.