Combine the onions and herb salt and salt in a large saucepan with enough water to cover. Bring to a boil over medium heat, and let boil until the onions are softened. Drain well, cut in half crosswise. Carefully remove the centers, leaving the three outermost layers of the shell. Arrange the shells upright in a baking dish. Finely chop the onion centers and set aside. Place the carrots and a pinch of salt in a small saucepan, and add just enough water to cover them. Place the spinach in a large sauce pan, bring to a boil over medium heat, and sprinkle with salt. Sprinkle lightly with water. Cover and cook over high heat, turning the spinach frequently, until wilted. Transfer to a colander and drain, removing as much water as possible. Cut the spinach into shreds. Heat the oil in a large skillet over medium heat. Add the chopped onion and garlic, and saute until soft. Add the carrots, raisins, dill, parsley, sugar and walnuts and continue cooking until carrots are tender. Increase the heat to high, add the spinach, and cook for 2 minutes, stirring constantly. Remove from heat and cool. Taste and adjust the seasoning. Preheat the broiler. Divide the mixture among the onions. Combine the cheese and breadcrumbs, and sprinkle over the tops. Broil until the tops are golden. Serve immediately.