In a 6-quart slow cooker, stir together the lamb, vinegar, brown sugar, coriander, cumin, cinnamon, pepper, fennel seeds, cardamom, saffron, cloves, and 1 tsp. salt until the meat is thoroughly coated in the spices.
In a large skillet, heat the oil over medium heat. Add the onions, ginger, and garlic. Cook, stirring often, until the onions are translucent, about 3 minutes.
Scrape the contents of the skillet into the slow cooker. Stir in the apricots, almonds, and tomato sauce. Cover and cook on low until the meat is very tender, about 6 hours. Remove the meat with tongs and separate the meat and bones, discarding the bones. Degrease the sauce, if necessary, by laying a paper towel on the surface to soak up the fat, then remove and discard it. Repeat with another paper towel, if needed. Return the meat to the sauce and season to taste with salt. Serve.
Since the curry is sweet, serve it over cooked long-grain brown rice for a nutty, earthy flavor, or with couscous or steamed, stemmed spinach.