Black Roasted Cod with Sea Beans and Oysters

Put oven rack in middle position and preheat oven to 450°F.
Cook sea beans in a 2-quart saucepan of boiling (unsalted) water 1 minute, then drain in a colander. Quickly transfer to a bowl of ice and cold water to stop cooking. Drain, then pat dry with paper towels.
Drain oysters in a sieve set over a bowl and reserve their liquor.
Pat fish dry and sprinkle with salt and pepper.
Heat oil in a 12-inch ovenproof heavy skillet over moderately high heat until hot but not smoking, then cook fish, skinned side up, until undersides are browned, 2 to 3 minutes. Turn fish over and transfer skillet to oven, then roast until fish is just cooked through, 9 to 11 minutes.
While cod is roasting, cook shallot in 3 tablespoons butter, covered, in a 10-inch heavy skillet over low heat, stirring occasionally, until softened but not golden, 2 to 3 minutes. Add lemon juice and oyster liquor and bring to a simmer over moderate heat. Add oysters and season lightly with salt and pepper if desired, then cook at a bare simmer, covered, until just barely firm, 1 to 2 minutes. Remove from heat.
Center pieces of cod on 4 large plates (reserve skillet) and arrange sea beans and oysters around fish. Discard fat from 12-inch skillet and add oyster cooking liquid. Bring to a boil over high heat and swirl in remaining tablespoon butter until incorporated. Spoon sauce over seafood and serve immediately.