How to Make It
In a small skillet, toast the coriander, cumin and fennel seeds over moderate heat, shaking the skillet, just until fragrant, about 3 minutes. Transfer to a spice grinder or mortar, add the crushed red pepper and grind to a powder. Return the ground spices to the skillet. Add 2 tablespoons of the olive oil and cook over low heat just until warmed through. Pour the oil through a very fine strainer or a tea strainer and keep warm.
In a large nonstick skillet, heat the remaining 1/2 tablespoon of oil until shimmering. Season the fish with salt and pepper and cook over moderately high heat until browned on the bottom, about 5 minutes. Turn and cook the other side until browned and the fish is just cooked through, about 3 more minutes. Transfer the halibut to warmed plates, drizzle with the spiced oil and serve.