To marinate the lamb, place the lamb fillets, vinegar, oil and garlic in a bowl. Toss to coat. Cover and set aside for 30-60 minutes.
Preheat oven to 200°C. Spread the bread cubes out over a large baking tray. Bake, turning once, for 8-10 minutes, until golden brown. Set aside.
Heat a large non-stick frying pan over a medium-high heat. Drain the lamb fillets. Add to the pan and cook for 2-3 minutes each side. Transfer to a plate and set aside to rest for 5 minutes. Diagonally slice the lamb.
Place the rocket leaves, bocconcini, capsicum, olives and bread cubes in a serving bowl. Toss well to combine. Whisk the vinegar and oil together. Season well with salt and pepper. Add the lamb and dressing to the salad. Toss well to combine. Serve immediately.