1. In the jar of a blender, combine all the marinade ingredients and whirl until smooth. Pour marinade into a medium glass baking dish. Lay the halibut filets into marinade, cover and refrigerate. Let marinate in the refrigerator, turning occasionally, for 8 hours, preferably for 2 days.

2. Fill a wok with enough water to come up 2 inches and bring to a boil. Meanwhile, bring to a boil over high heat. Meanwhile, lay four 10-inch X 10-inch squares of parchment paper or aluminum foil out on a work surface. Place a piece of halibut in the center of each square. Divide the squash equally between the four packets. Tuck 2 mushrooms and 2 bok choy halves around each piece of fish. Spoon 4 tablespoons of the marinade over each piece of fish. Gather sides of the parchment up and over the fish and squeeze together to form a waist, being sure packet is sealed.

3. Place two fish packets on each of two tiers of a bamboo steamer. Carefully place over the boiling water. Cover the steamer and cook until fish is opaque in the center, 5-8 minutes, depending on the thickness of the fish.

4. To serve, transfer each packet to a serving plate and carefully cut packet open allowing the steam to escape.