Grease a microwavable bowl with cooking spray and preheat the oven to 350°F (180°C), if baking it.
In a bowl, mash the banana, then add egg, Greek yogurt, maple syrup to taste, vanilla extract and a pinch of salt.
Stir in oat flour, protein powder (or more oat flour) and baking powder. Mix until a smooth batter forms - if it is too thick, gradually add 1–2 tbsp of milk as needed.
Transfer the batter to the prepared bowl and sprinkle with chocolate chips on top, if desired.
Microwave on high for 90 seconds to 2 minutes. If the batter rises too much, pause and restart in short intervals.Alternatively, bake in hot oven at 350°F (180°C) for 20–25 minutes or until set. Serve warm with your favorite toppings