Tear romaine in bite sized pieces and set aside. Mix lemon juice, sugar, ketchup, worcestershire and mustard and set aside. Turn wok on high until hot. Add oil, when oil is hot add onion and stir fry about 1 minute until onion is limp. Add lemon juice mixure. When mixture boils, add romaine. Remove from range. Add sprouts and croutons and toss util lettuce is coated with dressing.