Heat the olive oil in a large flameproof casserole (cocotte) and brown the meat, garlic and onions. Add the carrots, thyme, bay leaf and enough water to cover the meat by at least a couple of centimetres. Bring to a simmer and remove any scum that rises to the top. Once all the scum is removed, cover the pan. Cook until the meat is tender, 1 1/2 to 2 hours.
About 5 minutes before serving, add the beans and peas to the lamb. Cook until the vegetables are tender.
Season with salt and freshly ground black pepper, and serve straightaway.