Put the pineapple and the water in a saucepan and bring everything to a boil. As soon as the water boils, add the oatmeal, the raisins, the cinnamon and the brown sugar. Reduce the heat and let everything simmer gently for about 5 minutes.
Remove the saucepan from the heat and let it rest for another 5 minutes.
Arrange the porridge in a bowl. If you like, you can add a dash of milk over the finished oatmeal.