1 1/2 lb. beef tenderloin or sirloin, cut across the grain into thin strips
5 Tbs. soy sauce
2 Tbs. rice wine or dry sherry
4 Tbs. water
2 Tbs. Worcestershire sauce
2 tsp. Asian sesame oil
1/2 tsp. sugar
1/2 tsp. cornstarch
1 tsp. freshly ground black pepper
2 Tbs. corn or peanut oil
1 large yellow onion, thinly sliced
1 orange or yellow bell pepper, seeded and sliced (optional)
1 Tbs. grated fresh ginger
Red pepper flakes, to taste (optional)
Steamed rice for serving