Puree the vinegar with all the other ingredients up to and including the salt.
Remove the meat from the fridge approx. 1 hr. prior to grilling. Brush the meat with oil, season, cover and grill over/on a medium heat (approx. 200 °C for approx. 6 mins. on each side. Remove the meat from the grill, cover with foil and leave to rest for approx. 10 mins.
Mix the lettuce, radish and avocado with half of the chimichurri sauce. Carve the meat, serve with the salad, drizzle with the remainder of the chimichurri sauce.