Preheat the BBQ grill. Brush the rump cap steak with olive oil and season with plenty of salt and pepper. Place on a long metal skewer and grill for 5 minutes, turn, cook for a further 5 minutes, turn, cook for 3 minutes, turn, and cook for a further 3 minutes. Test for doneness. Remove and allow to rest.
While the steaks are cooking make the sauce by placing the remaining ingredients into a food processor and blend until smooth. Slice the meat and serve with the sauce.