Put the sugar in a saucepan with the water. Heat slowly until the sugar has dissolved, then add the chillies, bring to the boil and boil rapidly until the liquid becomes syrupy. Leave to cool.
Stir the lime rind and juice into the cooled syrup. Lay the pineapple slices on a plate and drizzle the syrup over. Serve chilled with a dollop of ice cream, if liked.