Place the lamb in the slow cooker and add diced onion, garlic, wine, mint, rosemary and tomatoes. Combine french onion soup mix and tablespoon of beef stock powder in a cup of water and add over lamb.
Cook on high for 1 hour and 4 hours on low before adding to the oven for half hour to brown the lamb a little.
At the end I used 4 tablespoons of gravy powder to 2 cups of stock and made a beautiful gravy for the lamb.