Make the sauce by mixing together all the ingredients in a small bowl. Then set aside until ready to eat.
Pat the steaks dry with kitchen paper. Mix together the olive oil, spices and a little salt, then rub or brush over both sides of meat. Heat a griddle pan or barbecue until hot and smoking. Cook the steaks for 3 mins each side for rare, 4 for medium and 5 for well done. Then remove to a board and leave to rest for a couple of mins. Slice the steaks on the diagonal into thin pieces and serve with the chimichurri sauce to spoon over.