Heat oil in heavy large ovenproof skillet over medium-high heat. Sprinkle swordfish with salt and ground mixed peppercorns. Add swordfish to skillet. Cook until browned, about 3 minutes. Turn swordfish over and transfer to oven. Roast until just cooked through, about 10 minutes longer. Transfer swordfish to plates. Add seasoned butter to same skillet. Cook over medium-high heat, scraping up browned bits, until melted and bubbling. Pour butter sauce over swordfish and serve.