Rinse the fish, dab dry with kitchen paper and cut in half lengthwise. Clean the courgettes, wash them thoroughly and peel the courgettes into strips with a peeler. Wash parsley and dill, dab dry and chop finely.
Chop the cucumber very finely. Mix mustard, oil, cucumber, parsley and dill. Season with salt and pepper. Brush one side of the fish fillets with the herb mixture, roll them up and stick them together with wooden skewers.
Bring lemon juice, 500 ml water, wine, peppercorns, salt and bay leaf to the boil. Put the fish rolls in and let them simmer for about 8 minutes. Meanwhile cook the courgettes in boiling salted water for about 3 minutes, drain and drain.
Arrange on a plate and keep warm. Remove the fish rolls from the stock and place them on the zucchini. Measure 150 ml of stock and put aside. Melt the fat in a saucepan, dust with flour and sauté.
Deglaze with 150 ml fish stock and cream. Bring to the boil while stirring. Simmer for 1-2 minutes and season with salt, pepper, sugar and tarragon. Drizzle fish rolls with some sauce and serve garnished with dill, tarragon and lemon slices as desired.
The rest of the sauce extra is fine. Baguette tastes good with it.