Remove the steak from the refrigerator at least 30 minutes before you want to eat. Preheat your grill pan or barbecue to medium-high.
Rub the steaks all over lightly with oil and season them generously with salt and pepper. Cook the steaks over a medium-high heat for 2 minutes, then turn and cook for a further 2 minutes. Turn again, this time at a 90 degrees angle, and cook for another 2 minutes. Turn for a final time, and cook for 2 more minutes.
The steaks should be cooked medium-rare, and be neatly crosshatched with marks from the griddle. Use the thumb-to-finger test for doneness, or check the interior of the meat with a meat thermometer.
Transfer the steaks to a warm plate and cover them loosely with foil. Leave them to rest for 4 minutes before serving.
Salsa verde; Chop the olives, gherkins and parsley separately.