Put water to boil in a saucepot and add salt to taste.
Peel then cut the potatoes into slices or into large dice and add to the boiling water. Boil for about 8 minutes then drain and set aside.
Put orange juice to boil in a separate saucepot. Add the sugar, margarine, orange rind, cinnamon powder and raisins and simmer until the mixture becomes syrupy.
Fold in the sweet potato and the diced pineapple, if used.
Spoon the mixture into a lightly greased casserole top with orange slices.
Place in a preheated oven 180°C (350°F) and bake for 10 minutes.