Prepare the ribs the night before: Trim the membrane from the back of 2 racks (about 4 pounds) St. Louis pork ribs. Then make the rub: Whisk 1 cup rice vinegar, 1/4 cup soy sauce, 3 tablespoons chopped ginger, 5 chopped garlic cloves, 1 tablespoon sesame oil and 1 teaspoon Chinese five-spice powder; coat the ribs with the mixture and refrigerate overnight. Preheat a grill to medium-high on one side and place a drip pan under the cooler side. Set the ribs over the drip pan (use a rib rack, if you have one). Cover, making sure the vent holes are directly over the ribs; cook for 3 hours, or until the meat pulls back from the bones. To make the sauce, whisk 1/2 cup hoisin sauce, 2 to 3 tablespoons Asian chili sauce and 1 tablespoon water; brush onto the meat and cook over direct heat until glazed. Cut the racks into ribs and sprinkle with sliced scallions and sesame seeds.