Preheat your oven to 180°C (350°F) and line a baking sheet with parchment paper.
In a bowl, mix the mashed bananas, melted butter, and brown sugar until smooth. Add the egg and vanilla, stirring until well combined.
In another bowl, whisk together the flour, baking soda, baking powder, and salt. If using oats, add them in this step.
Combine the dry and wet ingredients until just mixed. Gently fold in the chocolate chips, if desired.
Scoop tablespoons of dough onto the prepared baking sheet, spacing them apart slightly.
Bake for 10-12 minutes or until the edges are golden and the centres are set. Cool on a wire rack.