Sauté the undrained oysters in a saucepan until the edges curl. Remove from the heat and drain well. Place the drained oysters in a large shallow gratin dish.
Blend the parsley, garlic and mushrooms in a food processor until the parsley is finely chopped. Add the butter, salt, pepper and nutmeg and blend well. Add the bread crumbs and blend well.
Spread the sauce over the oysters. Broil until brown and bubbly.