In a 3-quart baking dish heat the oil over high heat until it is hot. Brown and dry lamb in batches, transferring it with a slotted spoon as it is browned to a bowl. In the fat remaining in the dish cook the onion over low heat, stirring occasionally, until it is softened, add garlic and the ginger, and cook the mixture stirring, for 3 minutes. Add the cumin and coriander and cook the mixture, stirring for 1 minute. Add the stock, whisking, and simmer the mixture for 5 minutes. Add the lime juice, the chilies, the tomatoes, the lamb and any juices that have accumulated in the bowl, add salt and pepper to taste and simmer the mixture, covered, for 1 hour and 30 minutes, or until lamb is tender.