In a large, heavy-bottomed stockpot or Dutch oven, heat the olive oil over medium heat.
Add the onion, garlic, ginger, and chile. Cook, stirring occasionally, until onion begins to soften (about 5 minutes).
Season the lamb with salt and pepper. Add to the stock pot and brown on all sides.
Add the mustard, red wine vinegar, tomato sauce, and spices to the stock. Cook, stirring occasionally, for 3-5 minutes, or until spices are fragrant.
Add the beef stock, potatoes, and bay leaf. Add water if necessary to just cover potatoes and meat.
Cook with the lid on for 45 minutes to 1 hour, or until lamb is tender.
Serve over rice or with flatbread, such as naan.
Notes
To adapt this for the crockpot, season the lamb and brown it in olive oil on the stove. Add the browned lamb and all remaining ingredients to the crockpot. Cook on low for 6-8 hours.
You can make this dish with chicken or beef in place of lamb.