1) Preheat the oven to 400°F.
2) Line a small baking pan with the exact size of aluminium foil.
3) In a bowl, mix together mushrooms, tomatoes, onions, salt, pepper and herbs.
4) Arrange the fish in a baking dish.
5) Spoon the mushroom mixture over the fish and tuck the sides of the foil to make package.
6) Bake for 20 minutes or until the fish is tender.
7) Serve the fish in package, and just tear open the foil.
8) Cooked or canned peas can be served with the fish.