Heat butter in the frying pan and fry leek and zucchini, about 5 min, add herbs, salt and white pepper.
Cut square of aluminum foil, 20cm x 20cm. Arrange 2 slices of lemon, atop with bream, cover with fried vegetables, pour with 2 table spoons of cream and close the pouch.
Repeat with remaining bream fillets.
Bake pouches about 25 minutes in preheated oven, in 180 C degrees.