Heat oven to 400° F. Tear off four 15-inch squares of parchment paper or aluminum foil and arrange on 2 baking sheets. Divide the bok choy and bell pepper evenly among the squares. Place a halibut fillet on each mound of vegetables and sprinkle with the black pepper. Top with the scallions and zest.
In a small bowl, combine the soy sauce, vinegar, oil, and ginger. Spoon the mixture evenly over the halibut. Top with 4 more squares of parchment or foil and fold the edges over several times to seal. Bake for 15 minutes. Transfer each packet to a plate. Serve with a knife to slit the package open, and be careful of the steam that will escape.
Tip: This beautiful meal works just as well with other types of seafood. Next time, try cod, salmon, sea scallops, or peeled and deveined shrimp.