Preheat the grill to medium-high. In a small bowl, whisk together the ketchup, sugar, soy sauce, vinegar, ginger, pepper and garlic. Set aside. In a mixing bowl, combine the ground chicken and breadcrumbs along with half of the prepared sauce. Divide into 4 patties, and with your thumb, make a shallow indention in the center. Grill 5 minutes, then turn and baste with the remaining sauce. Add the pineapple slices to the grill and continue cooking until the patties are fully cooked (165 degrees) and the pineapple is charred.
During the last minute of cooking, place the buns cut side down on the grill to toast. Assemble the patties on mayonnaise-smeared buns with lettuce, onions and the grilled pineapple. Serve warm.
Recipe by The Tennessee Magazine at https://www.tnmagazine.org/bring-on-the-burgers/