Rinse fillets and pat dry. Fry in 1 tablespoon of hot oil for 5-7 minutes on each side until brown
Clean and wash the fennel and put aside some tender greens for garnishing. Slice or cut the fennel into thin slices. Squeeze 1 orange. Peel 1 orange so that the white skin is removed. Cut out the fillets between the parting skins, collect the juice
Season the meat with salt and pepper and take it out. Dissolve the gravy with orange juice. Stir in vinegar and 4 tablespoons of oil. Season to taste with salt, pepper, sugar and mustard. Mix marinade and fennel and let it stand for about 30 minutes
Peel onion and cut into fine rings. Add the orange fillets to the fennel. Cut the meat open. Arrange everything, garnish with fennel green and possibly crushed pink berries. Ciabatta goes well with it