Mix lemon juice, grated onion, garlic, and a mixture of salt, dry mustard, chili powder, cumin, thyme, and seasoned pepper.
Pour over lamb in a large shallow dish or pan.
Cover and marinate in refrigerator 6 to 8 hours, or overnight; turn occasionally.
Remove spareribs from marinade and place on rack in shallow roasting pan.
Roast at 325Â°F 1 1/2 hours, basting occasionally with marinade.
Sprinkle spareribs with paprika; roast 1/2 hour longer, or until tender.
Place ribs in a serving dish and garnish with parsley sprigs.