Beef Bulgogi Burgers

Name: Beef Bulgogi Burgers
Prep time: 20 min
Cook time: 10 min
Total time: 30 min
Cuisine: Asian, Korean
Ingredients: 3 tablespoons soy sauce; 1 tablespoon Asian/toasted sesame oil; 1½ tablespoons packed dark brown sugar; ¼ teaspoon crushed red pepper flakes; ¼ teaspoon ground ginger; 2 cloves garlic, minced; 1 slice white or whole wheat sandwich bread, crusts removed and torn into ¼-inch pieces; 1½ pounds 85% lean ground beef; ½ cup chopped scallions, from 4 to 5 scallions; 5 hamburger buns; Lettuce leaves, for serving (optional); ¾ cup mayonnaise, best quality such as Hellmann's or Duke's; ¼ cup Asian chili sauce, such as Sambal Oelek (available in Asian aisle of most supermarkets); ¼ teaspoon granulated sugar