Mash butter, parsley, garlic, 1/2 teaspoon ground mixed peppercorns, and lemon peel in a small bowl. Season to taste with salt.
Heat oil in heavy large ovenproof skillet over medium-high heat. Sprinkle fish with salt and ground mixed peppercorns. Add fish 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 the same skillet. Cook over medium-high heat, scraping up the browned bits until melted and bubbling. Pour butter sauce over swordfish and serve.
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