Preheat broiler. Line a large roasting pan with the sliced fennel. Make 3 (3-inch) long incisions on each side of the fish. Coat fish with olive oil and insert a slice of fennel into each incision. Place fish over fennel in the roasting pan. Surround and cover the fish with all remaining ingredients, including the herb stems and entire heads of garlic. Pour 1 cup water into the roasting pan around the fish. Broil for 30 minutes or until flesh is cooked through and flaky. Serve.