Thinly slice sirloin against grain in 1 inch wide strips. Cut each water chestnut in half. In a large skillet or wok, quickly brown sirloin in hot oil. Stir in chestnuts, carrots, onion, garlic and ginger until onion is soft. Stir in pepper and lettuce for one minute. Stir in marmalade and soy sauce. Cook, stirring about 2 minutes. Serve at once. Makes 4 servings.