How to Make It
Preheat the oven to 400°. Spread the shredded coconut in a pie plate and toast for 5 minutes, or until lightly browned. Increase the oven temperature to 450°.
In a food processor, combine the cilantro stems with the onion, garlic, 1 chile, the lemongrass, ginger, lime zest and nutmeg and process.
In a medium saucepan, heat 1 tablespoon of oil. Add the cilantro paste and cook over low heat, stirring occasionally, until very aromatic, about 10 minutes. Add the coconut milk and fish sauce and simmer for 10 minutes longer.
In a saucepan of boiling salted water, blanch the bok choy for 2 minutes. Drain in a colander, then rinse in cold running water; pat dry. Spread the bok choy in a 9-by-12-inch gratin dish.
In a large skillet, heat 1/8 inch of oil. Season the halibut steaks with salt and add 2 of them to the skillet. Cook over high heat, turning once, until golden, about 2 minutes per side. Set the fish steaks on the bok choy and repeat with the remaining halibut.
Add the lime juice to the sauce and season it with salt. Strain the sauce over the fish and top with the scallions. Cover with foil and bake for 8 minutes, or until the fish is opaque throughout.
In a bowl, combine the remaining chopped chile with the cilantro leaves and toasted coconut. Transfer the halibut steaks to plates and spoon the sauce over the top. Sprinkle the cilantro-coconut salad over the fish and serve at once.