1Place a large rimmed baking sheet in the oven and preheat to 400°F.
2Rub both sides of fish with 1 tablespoon oil; season with ¾ teaspoon pepper and ¼ teaspoon salt.
3Combine broccoli rabe, the remaining 1 tablespoon oil and ¼ teaspoon each salt and pepper in a large bowl. Massage the broccoli rabe until evenly coated.
4Place the fish and broccoli rabe on the hot baking sheet. Roast until the fish is just cooked through and the broccoli rabe is tender, 8 to 10 minutes.
5Meanwhile, mix butter, lemon zest, garlic, capers and parsley in a small bowl.
6To serve, toss half the piccata butter with the broccoli rabe and dollop the rest on the fish.
Tips: Swordfish populations have increased to a more sustainable level—choose handline- or harpoon-caught from the North Atlantic and Eastern Pacific. Swordfish is high in mercury, so it's best to eat it only occasionally. Women who may become pregnant, breast-feeding mothers and young children should avoid swordfish. Halibut is a good alternative.