Preheat oven to 425. Place eggplant halves, skin side down, in an ovenproof pan that holds them snugly. Brush the flesh with half the olive oil and season with 1/4 teaspoons salt and plenty of black pepper. Roast for 20 minutes, until tops are golden brown. Remove from oven and allow to cool slightly in the pan.
Reduce the oven temperature to 375 after removing the pan of eggplant.
While the eggplants roast, start the stuffing: heat the remaining olive oil in a frying pan. Mix together the cumin, paprika, and ground cinnamon and add half the mixed spices to the pan, along with the onions. Cook on medium for about 8 minutes, stirring often so spices don't burn, then add the lamb, pine nuts, parsley, tomato paste, 1/2 teaspoons of the sugar, 1/4 teaspoons salt, and some black pepper. Continue to cook and stir another 8 minutes to cook the meat through.
Place the remaining half of the spice mix in a bowl and add the water, lemon juice, tamarind, the remaining 1/2 teaspoons sugar, the cinnamon stick, and 1/4 teaspoons salt. Mix well and pour this mixture into the bottom of the eggplant baking pan.
Spoon the lamb mixture on top of the eggplant halves. Cover the pan tightly with aluminum foil, return to the oven, and bake for 75 to 90 minutes,basting the eggplants with the sauce every 30 minutes and adding more water if necessary. The eggplants should be completely soft and the sauce thick at the end of the cooking time. Allow to cool slightly before serving, or serve at room temperature.