Step 1Combine the ginger, soy sauce, rice vinegar, water, sugar, garlic and sesame oil in a small bowl, then set them aside while you prepare the fish and vegetables.
Step 2Place the carrots in the top of a steamer over simmering water. Steam the carrots 5 minutes. Push the carrots to one side of the steamer and add the halibut steaks and mushrooms. Place the lemon slices and sprigs of cilantro on top of the fish. Put the cover back on the steamer and steam the fish another 5 to 8 minutes.
Step 3After 5 minutes, check to see if the fish is done: Pierce the center of each steak with a knife or fork and pull it open slightly; the flesh should be opaque and moist. If the fish is done, remove it to a platter, cover and keep warm.
Step 4Add the bok choy to the steamer and cook until it's limp yet tender, 3 to 4 minutes. Remove the vegetables from the steamer. Arrange the fish and vegetables on serving plates and spoon a little of the ginger soy sauce over the top.