Heat oven to 350° F. Place the ribs in a large roasting pan and season with 1 teaspoon pepper.
In a small bowl, combine the hoisin sauce, soy sauce, ginger, and garlic; spoon half of the glaze over the ribs. Cover the pan tightly with foil and bake until the ribs are tender, 40 to 45 minutes.
After the ribs have been cooking for 20 minutes, combine the rice, 1 1/2 cups water, and 1/2 teaspoon salt in a medium saucepan with a tight-fitting lid and bring to a boil. Stir once, cover, and reduce heat to low. Simmer for 18 minutes. (Do not lift the lid or stir!) Remove from heat and let stand, covered, for 5 minutes; fluff with a fork before serving.
Heat the broiler. Spoon off and discard all but 1/2 cup of the rib pan drippings. Cut the racks of ribs into individual ribs, return to the roasting pan, and brush with the remaining glaze. Broil until just beginning to char, 2 to 3 minutes. Serve the ribs over the rice, drizzle with any cooking juices, and sprinkle with the scallions.