Cover with a plate or cling film and leave in the fridge overnight or for at least 5 hours before eating.
Remove from the fridge just before eating and serve with toppings of choice.
It might seem like you’ll be adding a lot of liquid, but it all gets soaked up by the oats. If the oats still look dry the next morning, you can add extra milk before eating.Adding the mashed banana means that the oats will have turned brown by the time you eat them the next morning. This is completely natural, it is still ok to eat and the taste won’t be at all affected.