Cook the lentils as per packet directions. Drain.
Meanwhile, place the onion, tomato, vinegar and oil in a bowl. Add the warm lentils and toss to combine. Set aside for 10 minutes.
Cook the broad beans in boiling water until just tender. Drain. Set aside to cool slightly. Add the beans and parsley to the lentil mixture.
Heat a large non-stick fry pan on high heat and spray with olive oil. Cook the lamb for 3-4 minutes each side or until cooked to your liking. Transfer to a place. Cover loosely with foil and set aside to rest for 3 minutes.
Thinly slice lamb. Divide the lentil mixture amongst plates and top with lamb.