Papaya, oat flakes and cinnamon blended with milk into one thick glass. It takes five minutes, it needs no cooking, and it is better drunk straight away: papaya carries an enzyme that turns the milk bitter if the glass sits around.
Drink it fresh rather than making it ahead. Papaya contains papain, an enzyme that breaks down protein, and it keeps working in the glass: after an hour or two with milk the smoothie turns noticeably bitter. Refrigerating slows it down but does not stop it. If you want it thicker, use frozen papaya cubes instead of ice, which chills it without watering it down. If it comes out grainy, the oats simply need longer in the blender, or you can soak them in the milk for ten minutes first.