FOR THE ORANGE-TAHINI SAUCE: In a blender or food processor, combine all ingredients. Refrigerate until ready to use. FOR THE FILLING: Melt the butter or heat the oil in a medium saucepan. Saute the onion until soft, about 10 minutes. Add the rice and stir to coat with the butter. Add the broth, bring to a boil, cover, and simmer over low heat until rice is tender and liquid is absorbed, about 45 minutes. Let cool to room temperature. In a large bowl, toss together the cooked rice, Orange-Tahini Sauce, chickpeas, and raisins. Prepare the oranges for stuffing by slicing off the rounded ends so that each half stands squarely on a plate. Using a paring knife, carve out the fruit, cut it into bite-size sections, and toss it into the rice mixture. Once the fruit has been removed, cut away as much of the white portion of the peel as possible, leaving the shell intact. Set the orange shells on a serving dish and fill them with the rice mixture. Garnish each with a sprinkling of sesame seeds and scallions topped with a whole cilantro leaf.