Cut off the green from the fennel and keep it. Then remove the stalks, quarter the tuber and slice it into wafer-thin slices. Finely dice the onions and garlic, halve the cherry tomatoes. Put the fennel with onions, garlic, tomatoes, olives and fennel seeds in a bowl, season with salt and pepper and mix together.
Spread out 4 pieces of aluminum foil with a size of approx. 30 x 40 cm and brush with a little olive oil. Spread the mixed vegetables on top. Season the fish fillets and place them on top and drizzle with a few drops of olive oil.
Fold up the sides of the aluminum foil, put 2 tablespoons of stock in each packet and then close the foil on top. Place the parcel on a baking sheet.
Cook the parcels on the tray in a preheated oven at 215 ° C for 20 to 25 minutes.
To serve, chop the fennel greens and sprinkle over the fish.