Heat a wok or large skillet over medium heat. Add oil and swirl to coat. When oil is hot but not smoking, add onion and stir-fry for 3 minutes. Add green pepper and stir-fry for 2 minutes. Add white ends of the bok choy and the broccoli and stir-fry for 2 minutes. Stir in green bok choy leaves, water, hoisin sauce and soy sauce. Cover and cook for 3 minutes or until broccoli is tender-crisp.
Transfer to a serving dish, drizzle with sesame oil and sprinkle with sesame seeds