Season the swordfish steaks with salt and pepper and place in a shallow dish. Mix all the marinade ingredients together, and pour over the swordfish. Leave to marinade for no longer than 15 minutes (you don’t want to risk the lemon “cooking” the fish).
Meanwhile, to make the sauce, blanch the broad beans in a pan of boiling water for 2 minutes, then drain and set aside.
Make the gremolata by mixing together the lemon zest, olives, capers and parsley.
Heat a tablespoon of olive oil in a heavy-based frying pan. When the pan is very hot, add the swordfish steaks and fry for 3–4 minutes on each side.
Remove from the pan and leave to rest while you finish the sauce. Deglaze the pan with the white wine, then add the butter. Swirl until the butter has melted, then add the blanched broad beans. Heat through.
Serve the swordfish with the sauce spooned over and the gremolata on the side.