1) Cut the lamb into 4cm cubes. You should have about 40 cubes. Combine the garlic, rosemary, thyme, olive oil, red wine, vinegar and salt in a medium bowl. Add the lamb cubes, cover with cling film and refrigerate overnight or for up to two days, turning occasionally.
2) Heat a charcoal barbecue with coals. Spread the coals in one tight layer on the griddle.
3) Cut the red onions into quarters and separate each quarter into three or four sections. Loosely thread three or four pieces of lamb alternately with sections of onion on skewers. Sprinkle both sides of the lamb with salt and pepper. Next, place four or five cherry tomatoes on separate skewers, threading the skewers through the stem of the tomato. Rub the tomatoes with olive oil and sprinkle with salt and pepper.
4) First, place the lamb skewers on the hot griddle and cook for 10 to 15 minutes, turning two or three times, until the lamb is medium rare. Approximately five minutes before the lamb is done, place the tomato skewers on the griddle, turning once, until seared on the outside but still firm inside.
5) Serve the kebabs with the sauce on the side.
For the sauce:
1) Bring the chicken stock, olive oil and lemon juice to a boil in a medium pot. Lower the heat and simmer for 5 minutes, until reduced by half. Add the rosemary, salt and pepper.