Rock cod, sometimes sold as rockfish, is common along the Pacific coast. It is not related to true cod from the Atlantic.
3 scallions, trimmed
3''-4'' piece ginger, peeled
3 tbsp. reduced sodium Japanese soy sauce
3 tbsp. shaoxing (Chinese rice wine)
2 tsp. oyster sauce
1 2-lb. whole rock cod, sea bass, or red snapper,
cleaned and scaled
6 sprigs fresh cilantro
2 tbsp. peanut oil
1. Trim off scallion greens and set aside, then slice white parts lengthwise into long, very thin strips and set aside. Slice ginger lengthwise into thin pieces, set 4 or 5 aside, then slice remaining pieces lengthwise into very thin strips and set aside. Mix together soy sauce, shaoxing, and oyster sauce in a small bowl and set aside.
2. Arrange scallion greens on a heat-proof platter and lay fish on top. Tuck thin pieces of ginger inside fish cavity and set platter aside. Pour water into a wok or wide, shallow pan to a depth of about 2'', set a round cookie rack over water, and bring to a boil over high heat. Set platter with fish on rack, cover, and steam until fish is just cooked through, 10-12 minutes. Remove platter from wok and pour off any accumulated juices and foam.
3. Pour reserved sauce over fish, then scatter reserved scallions, ginger, and cilantro on top. Heat oil in a small pan over high heat until just smoking, then pour over fish.