Season the lamb.
Thinly slice the onion, garlic and pepper.
Heat half of the oil in a medium frying pan and seal the lamb on both sides, then transfer them to a plate.
Pour away the fat, then add the remaining oil to the pan, then gently sauté the onion for 3 minutes. Add the garlic, pepper, chilli flakes (if used) and cherry tomatoes. Saute for another 5 minutes or so.
Add the puttanesca sauce, cover and cook for 5 minutes, then add the lamb and cook for another 5 minutes. (If the sauce seems too thick add a drop of water or some passata.)
Finally, add the olives, some fresh herbs and serve.