I LOVE rhubarb and it's VERY good for you. When I was on a drastic diet some years ago and lost 3 stone in just a few months, I ate loads of rhubarb with a dab of plain yoghurt because it's very low in calories (as long as you don't add loads of sugar or cumble topping!).
Chocolate with a soft and delicate rhubarb filling would be delicious.