Special equipment: a 2 1/2-qt shallow ceramic or glass baking dish
Directions
Put oven rack in upper third of oven and preheat oven to 450°F.
Pat fish dry and sprinkle with salt and pepper. Heat 1 tablespoon oil in a 12-inch heavy skillet over moderately high heat until hot but not smoking, then sear fillets, skinned sides down, until browned well, 3 to 4 minutes. Transfer, seared sides up, to baking dish (reserve skillet), then top each fillet with a slice of lemon.
Add wine to skillet and bring to a boil, scraping up any brown bits. Boil 30 seconds, then pour around fish. Scatter olives around fish and bake, uncovered, until fish is just cooked through, 8 to 12 minutes.
Transfer fish to a platter, then whisk lemon juice, oregano, and remaining 2 tablespoons oil into cooking liquid in baking dish. Season sauce with salt and pepper and spoon over fish.