For the porridge, bring oatmeal to a gentle simmer with the milk and water over medium heat, turning down a bit after a few minutes to thicken to desired consistency.
Stir occasionally. Mash about 3/4 of the banana with a fork, slice remaining bananas.
Wash raspberries, put a few raspberries on the side, stir maple syrup into the finished porridge and mix the banana and raspberries into the porridge.
Put the remaining raspberries and the banana slices on top of the porridge.