In a large bowl, combine the ground cumin, ground coriander, ground turmeric, ground black pepper, ground cardamom, ground cloves, ground cinnamon, ground nutmeg, minced garlic, olive oil, lemon juice, and salt. Mix well to form a marinade.
Rub the marinade all over the lamb, making sure to cover it evenly. Let the meat marinate for at least 2 hours, preferably overnight, in the refrigerator.
Preheat your oven to 325째F (165째C).
In a large baking dish or roasting pan, place the quartered onions, quartered tomatoes, and bay leaves at the bottom.
Place the marinated lamb on top of the vegetables.
Add 1/2 cup of water to the baking dish.
Cover the baking dish tightly with aluminum foil.
Roast in the preheated oven for about 3-4 hours, or until the meat is tender and falling off the bone.
Increase the oven temperature to 400째F (200째C).
Uncover the baking dish and roast for an additional 20-30 minutes, or until the lamb is browned and crispy on the outside.
Remove the lamb from the oven and let it rest for a few minutes before serving.
Enjoy your meal!