1.Boil, steam or microwave potatoes until almost tender; drain, then cut in half lengthways.
2.Meanwhile, cook beef on heated oiled covered barbecue (or grill or grill pan) about 15 minutes until browned all over and cooked as desired. Remove from barbecue; cover beef, stand 10 minutes.
3.Combine potatoes with onion and oil in medium bowl. Cook potatoes and onions on heated barbecue about 5 minutes or until potatoes are browned and tender; season. Cover to keep warm.
4.Combine horseradish cream and herbs in medium bowl; season. Spread herb mixture all over beef.
5.Serve beef sliced, with potatoes and onions.