Combine oil, garlic and mustard in a bowl. Season with pepper. Place steak in a gastronome, pour over marinade. Leave in the coolroom for at least 1 hour.
Bring steaks to room temperature before cooking.
Remove steaks from marinade and cook on a hot grill for 2-3 minutes each side, or to an internal temperature of 49◦C. Leave to rest for half the cooking time.
Slice thinly and serve with chimichurrisauce and grilled vegetables.
