For the pickled salad: combine rice vinegar, sugar and salt in a small bowl and stir until sugar dissolves. Pour over vegetables, cover and refrigerate for 15 minutes to marinate. This can also be done the night before.
For the beef: combine marinade ingredients in a flat, non-reactive dish. Add beef and marinate for 30 minutes.
Pre-heat barbecue to searingly hot. Brush green onions with oil and chargrill on barbecue for 3 minutes on each side. Drain beef and flash cook on barbecue for a minute or so on each side, to sear, but do not cook through or the beef will toughen.
Serve brisket and green onions scattered with sesame seeds and pickled salad on the side.