Bring the water to the boil with the sugar. Reduce the heat, add the rhubarb, simmer for approx. 5 mins. until just soft. Drain the rhubarb, retain the rhubarb liquid, leave both to cool.
Combine the clotted cream, yoghurt and sugar, stir until smooth.
Place half of the sponge fingers along the base of the tin. Drizzle with a little of the reserved rhubarb liquid. Top with half of the strawberries and half of the cream. Arrange the rest of the sponge fingers on top and drizzle with the remainder of the rhubarb liquid. Top with half of the rhubarb and the remainder of the cream, cover and freeze for approx. 4 hrs.
Take the tiramisu out of the freezer approx. 15 mins. prior to serving, remove from the tin, top with the remainder of the rhubarb and strawberries. Cut the tiramisu into slices, plate up.