Bring large pot of water to boil; add salt and baking soda. Add Chinese broccoli and press down into boiling water. Cook 2-4 minutes until stems are just tender.
Drain Chinese broccoli and place in a bowl of cold water to stop cooking process. Drain and place on serving dish.
In a small bowl, mix together oyster sauce, soy sauce, sesame oil and mirin. Drizzle on top of cooked Chinese broccoli. Sprinkle with sesame seeds, if desired.