Mix the salt and pepper in a small bowl with the five-spice powder. Rub some of the mixture all over the ribs, and then store remaining rub in an airtight container for another use. Arrange the ribs in a single layer in a roasting pan and slow-roast for 2 hours.
To make Teriyaki Glaze: In a pot, combine the soy sauce, grapefruit juice, hoisin sauce, ketchup, rice wine vinegar, chile, garlic, and ginger over medium heat. Bring to a slow simmer and cook, stirring, until thickened, about 20 minutes. Reserve 1 cup of Teriyaki Glaze in a small bowl and set aside.
In the last 30 minutes of cooking, baste the ribs with the Teriyaki Glaze. When they are done, the meat will start to pull away from the bone. Just before you're ready to eat, baste the ribs with the Teriyaki Glaze again and stick them under the broiler for 5 to 8 minutes to make the spareribs a nice crusty brown. Separate the ribs with a cleaver or sharp knife, cutting at every second rib so there are 2 bones per piece. Pile them on a platter, and pour on the reserved Glaze. Sprinkle with sesame seeds and chopped cilantro.