Sauté the onion in the oil until soft. Add the rhubarb pieces and sauté. Pour in the red wine. Add the sugar and simmer for four minutes on low heat. Remove some of the rhubarb from the sauce and set aside.
Peel the ginger and grate finely. Add the ginger and mustard to the sauce form and mash it. Add the rhubarb pieces repeatedly.
Bring the vegetable soup to a boil, pour in the fish fillets and poach on a low heat with the lid closed for five minutes.
Make a mirror with the hot rhubarb sauce on heated plates. Arrange the fish fillets on it.
Tip: Serve with dry rice.
Tip: As an alternative to the fresh chives, you can also use the freeze-dried ones.