Melt butter or margarine, add mushrooms and cook 3 minutes over low heat. Stir in the flour and seasonings and then the milk and chicken stock. Continue stirring until sauce thickens. Add chicken and drained, cooked vermicelli or spaghetti and place in casserole. Sprinkle thickly with the grated cheese and bake in moderate oven (375 F.) about 20 minutes. Sprinkle with the chopped parsley. Yield: 4 servings.