Prepare Braising Liquid: Pour the oil, wine, and water into a large (13-inch) skillet, then add the fennel, tomatoes, garlic, and lemon slices. Season with salt and pepper. Cover and bring to a boil over high heat, then simmer over moderate heat until the tomatoes begin to fall apart and the fennel softens, 12 to 15 minutes.
Braise Fish: Sprinkle both sides of the fish with salt and pepper and arrange fillets in the pan, partially submerging them in the sauce. Cover and simmer until fish is opaque throughout, 6 to 8 minutes (or 8 to 10 for thicker fillets).
Serve: Spoon some of the braising sauce into a shallow bowl, then top with fish. Drizzle with olive oil, and sprinkle with pepper.
