For the striped bass: Preheat the oven to 325 degrees F. Spray the bottom of a large baking dish with the cooking spray.
Rinse the fish with cold water and pat it dry. Place it in the prepared baking dish. Season the fish with salt and white pepper. Scatter the sliced mushrooms in the dish. Sprinkle the sliced ginger over the fish and arrange the baby bok choy pieces around the fish, like a frame.
For the sauce: Stir together the soy sauce, chicken bouillon powder, Shaoxing rice wine, sugar and sesame oil in a small bowl. Pour this sauce over the fish, which will convert to aromatic steam, cooking the fish.
Pull a tight layer of plastic wrap over the baking dish and cover tightly with aluminum foil.
Bake until the fish reaches an internal temperature of 130 to 135 degrees F; the fish should flake apart gently, and the center should just be turning opaque, 15 to 18 minutes.
For after steaming: Check to see that the fish is done. Place the scallions on top of the fish and replace the foil to retain heat and moisture.
Combine the canola and sesame oils in a small saucepan and heat them to high until just smoking, about 2 minutes. Remove the foil and carefully drizzle the hot oil over the scallions and fish--it will sizzle. Finish by spooning the sauce over the fish.