In the bowl of a food processor, finely chop the pear, scallions, and garlic. Add the remaining marinade ingredients. Process until well combined.
Put the ribs in a large bowl and pour in the marinade. Mix well to coat the ribs evenly. Cover and refrigerate for 2 to 4 hours. Remove the ribs from the refrigerator and let stand at room temperature for 15 to 30 minutes before grilling.
Prepare the grill for direct cooking over high heat (450° to 550°F).
Brush the cooking grates clean. One at time, lift the ribs and let the liquid and solid bits fall back into the bowl. Discard the marinade. Grill the ribs over direct high heat, with the lid open, until they are nicely charred on both sides and cooked to a medium or medium-rare doneness, 3 to 5 minutes, turning occasionally. Remove from the grill and sprinkle with the sesame seeds.