Soak the dried fungus in boiling-hot water for 3–4 minutes, or until soft, then drain. Remove and discard the hard stalks and roughly chop.
Place the salmon fillets on a baking dish and sprinkle with the carrots, ginger, goji berries (if using), pepper, 1 tablespoon of the soy sauce and the fungus. Snap each coriander plant in half and place one on top of each fillet. Cover with foil and bake in a preheated oven, 180°C (350°F), Gas Mark 4, for 15–17 minutes or until a skewer will slide easily into the flesh and come out clean.
Remove the coriander plants. Place a fish fillet with some of the sauce on each warm serving plate. Pile a handful of watercress next to it. Serve the remaining light soy sauce separately in a small bowl. Alternatively, place each fish over boiled rice or cooked noodles, or serve with a vegetable dish such as stir-fried vegetables.