In a small bowl or jar, combine the oats, cinnamon, hazelnuts, and raisins, and stir to combine.
Add the grated apple and milk, and stir until everything is well mixed.
Transfer to the fridge and allow to sit for at least 2-3 hours, or allow to sit in the fridge overnight, this allow the oats to soften and become easier to digest.
When ready to eat, serve cold with a drizzle of honey and/or an extra splash of milk.
If desired, you can combine a larger batch of the rolled oats, cinnamon, hazelnuts and raisins and store it in an air-tight container or jar and simply add apple and milk when you are ready to eat.