How to Make It
Preheat the oven to 400°. In a small bowl, combine 2 tablespoons of the olive oil with the crushed garlic clove and the lemon zest. Let stand at room temperature for 10 minutes, then discard the garlic.
Meanwhile, in a large skillet, heat 1 tablespoon of the olive oil. Add the minced garlic, anchovy paste and crushed red pepper and cook over moderate heat, stirring, until fragrant, about 30 seconds. Add the escarole and cook over moderately high heat, stirring, until barely wilted, about 3 minutes. Season with salt and black pepper.
In a large, ovenproof skillet, heat the remaining 1 tablespoon of olive oil until shimmering. Season the halibut fillets with salt and black pepper and add them to the skillet. Cook over high heat until beginning to brown on the bottom, about 3 minutes. Transfer the skillet to the oven and roast the halibut for about 5 minutes, or until just white throughout.
Briefly warm the escarole over moderately high heat, until hot but still crisp-tender, about 1 minute. Spoon the escarole onto plates. With a spatula, transfer the halibut to the plates browned side up. Drizzle with the lemon-garlic oil and serve.