Place the ingredients in a high powered blender in the order listed. It’s important to put the oat milk in the blender first so that the blades can work properly. (If your banana is very ripe, you can skip the pure maple syrup.)
Starting at low speed and gradually increasing to high speed, process the mixture until smooth. This will take about 30 seconds. Taste the smoothie, and add the pure maple syrup if you think it needs it.