1. Cut ginger into thin slivers. Rinse green onions and trim and discard ends; cut onions (including tops) into 3-inch lengths, then cut lengthwise into shreds. Rinse bok choy and trim and discard stem ends; cut bok choy diagonally into 1/2-inch-thick slices.
2. Rinse fish and pat dry. Cut into four equal pieces, 3 to 4 inches square.
3. In a 12-inch frying pan or 5- to 6-quart pan over high heat, bring broth to a simmer. Form Shrimp and Pork Hash into four equal patties about 3 inches wide; set in simmering broth as formed. Cover, adjust heat to maintain simmer, and cook until patties are no longer pink on top, 3 to 4 minutes.
4. With a wide spatula, turn patties over; drape a piece of fish on each. Cover and simmer just until fish is barely opaque but still moist-looking in center of thickest part and patties are no longer pink in the center (cut both to test), 4 to 5 minutes longer.
5. Meanwhile, in an 8- to 10-inch frying pan over high heat, bring 1/4 cup water to a boil; add bok choy, cover, and cook just until bright green and tender-crisp to bite, about 2 minutes. Drain bok choy in a colander. Rinse and dry pan.
6. When fish and hash are done, with spatula, transfer one patty with fish to each of four wide, shallow bowls or rimmed plates. Top portions equally with bok choy and green onions. Drizzle evenly with soy sauce. Spoon hot broth equally around fish.
7. In frying pan, heat oil and ginger over high heat until oil ripples over pan bottom, about 30 seconds. Spoon hot oil and ginger equally over servings. Garnish with cilantro sprigs. Add salt to taste.