Preheat a barbeque or large char-grill pan over high heat. Brush beef on both sides with 1 tablespoon oil and cook for 3-4 minutes on each side, or until cooked to your liking. Set aside on a plate loosely covered with foil to rest for 5 minutes. Thinly slice beef.
Meanwhile, place sweet potato, zucchini and onion into a large bowl. Add 1 tbsp oil, season and toss to coat. Cook on same barbecue or char-grill pan over high heat, in batches, for 1-2 minutes each side, or until tender and lightly charred.
To serve, place rocket onto a large serving platter and top with vegetables and beef. Drizzle with remaining oil and lemon juice. Season. Sprinkle with lemon zest, feta and pine nuts. Garnish with mint leaves, to serve.
Brush each steak lightly with oil.
Preheat the barbecue to hot before adding the steak. The steak should sizzle as it makes contact with the plate or grill.
Cook one side until the first sign of moisture appears on the upper side, turn and cook the other side. Turn once only for rare and medium.
Test for doneness with tongs. Rare is soft when pressed, medium is springy but still soft and well done is very firm. Remove steak and cover loosely, rest in a warm place for a few minutes before serving.