Combine lamb, vinegar, garlic and half of the basil & mint mixture in a large bowl and toss to coat the lamb in the marinade. Cover and refrigerate for at least 3 hours or overnight.
Cook lentils in boiling water, uncovered, until tender. Drain.
Drain the marinade from the lamb then cook lamb on oiled grill plate (or grill or barbecue) until browned on both sides and cooked as desired. Cover lamb and stand for 5 minutes then slice thickly.
Place lentils in a large bowl with tomato, rocket, lemon rind and juice and remaining basil and mint. Toss gently to combine. Serve salad on plates topped with lamb slices.