Mix cornstarch and salt in a medium bowl. Add fish and toss to coat. Shake of the excess.
Mix 1 tablespoon soy sauce, fish sauce, sesame oil, black vinegar, and brown sugar in a small bowl. Set aside.
Heat half the oil in a wok on high. When hot, stir-fry ginger and chili for 1-2 minutes. Remove from wok and set aside.
In the same wok heat the rest of the oil. Fry fish for about 2 minutes on each side.
Add ginger/chili mixture and the soy sauce mixture. Let this bubble for a few seconds then toss until the fish is coated on all sides. Remove from the wok and set aside.
In the same wok add the bokchoy with the remaining tablespoon of soy sauce. Cover and let cook for about 30 seconds. Uncover, toss, cover and cook for another 30 seconds, then take off the heat. You want the bokchoy to be just cooked.
Arrange the bokchoy on a serving plate. Lay the fish on top of the vegetables. Top with a sprinkling of green onion.