Heat the sugar in a frying pan until melted. Add the porridge oats, stir and pour onto a non-stick baking sheet. Leave to cool and then break up. Heat the butter in a saucepan, add the rhubarb, caster sugar and ginger and cook over a low heat for five minutes, until softened.
Spoon the rhubarb into two glasses and sprinkle with a little of the caramelised oats. In a bowl, mix together the whipped cream and icing sugar, then spoon on top of the rhubarb. Scatter with the rest of the caramelised oats and serve.