In a small bowl, mix together the chopped garlic, olive oil, balsamic vinegar, lemon zest and basil leaves. Score the beef rib by placing a couple of shallow slits down each edge of the piece,
especially through any connective tissue. This will allow the marinade to soak into the meat well.
Set the beef rib into a baking dish and pour the marinade over. Turn the meat several times to coat completely. Cover with plastic wrap and place in the fridge for 2 to 3 hours, turning meat every hour.
Preheat oven to 200° C about 20 minutes before beef comes out of the refrigerator. Heat up the barbecue or hotplate on your stove. Lower heat to medium and grill each side of the rib for 2 to 3 minutes, taking care that any excess oil doesn't drip and flame up on the barbecue. This should take about 10-12 minutes total. Brush on some more of the marinade and then place beef back
in baking dish. Cook in the oven for 30 minutes for medium-rare.
Remove beef from oven and cover with aluminium foil to rest for 20 minutes. (It will continue to cook a little with the residual heat whilst resting, becoming nice and tender as the meat relaxes.)
Arrange the leafy greens on a large serving plate and arrange the sliced onion attractively around the edges.
Carve the rib into thin slices and place in the centre, on top of the greens. Drizzle with any meat
juices that remain. Place platter onto the table so your guest (or guests!) can help themselves. I guarantee they're going to want seconds!