Cook onion and green pepper in fat until tender. Heat soup in the top of a double boiler. Add cheese to soup and cook over boiling water, stirring constantly, until cheese is melted and mixture is smooth. Stir in mustard, worcestershire sauce, onion, and green pepper. Serve over toast pieces. Garnish with a sprig of parsley, if desired.
Calories per 1/3 cup serving: About 25