Peel and finely chop the onion and garlic cloves. Mix the olive oil in a bowl with the onion, garlic and the fresh herbs, season with salt and pepper.
Cut the rack of lamb into chops, making several cuts. This prevents them from bulging when grilling. Coat the cutlets with the herb marinade and leave to marinate in a bowl overnight.
Remove the lamb pieces from the marinade and drain well. Catch the marinade.
Grill the cutlets on the grill for about 8 minutes, turning several times and brushing with the marinade.