Rub the ribs all over with the five-spice powder; then season generously with salt and pepper. Put the ribs in a single layer in a roasting pan and slow-roast until they are almost tender, about 2 hours.
Meanwhile make the glaze. In a large bowl combine the soy sauce, grapefruit juice, hoisin sauce, ketchup, vinegar, brown sugar, chili, garlic and ginger in a saucepan. Bring the sauce to a simmer over medium heat. Cook until the sauce reduces and thickens then remove from the heat. Strain the sauce and reserve.
When the ribs are about 30 minutes away from being done, baste them with the teriyaki sauce. Cook until the meat pulls easily from the bone (about 1/2-inch of bone will show).
Just before serving, preheat the broiler. Baste the ribs again with the teriyaki sauce and brown them under the broiler for 5 to 8 minutes. (Keep a close eye on these guys - ribs go from perfectly crisp to perfectly burnt in seconds.) Separate the ribs with a cleaver or sharp knife, pile them on a platter, and pour on the remaining sauce. Sprinkle with sesame seeds, chopped cilantro, and green onion before serving.