1. Heat grill to medium-high.
2. Place bread in a food processor and pulse into fine crumbs. Transfer to a large bowl. Add ground turkey, water chestnuts, hoisin, scallions, ginger, garlic and salt; mix well. (The mixture will be moist.) Divide the mixture into four equal portions. Form into 1/2-inch-thick patties (see Tip).
3. Oil grill rack (See Grilling Tip). Brush patties with sesame oil. Grill until browned and no longer pink in the center (165°F), about 5 minutes per side.
4. Meanwhile, prepare Sesame Mayonnaise to serve with the burgers.
Tip: When forming burger patties, make them thinner at the center to prevent them from steaming as they cook.
Ingredient Note: Hoisin sauce is a dark brown, thick, spicy-sweet sauce made with soybeans and a complex mix of spices. Look for it in the Chinese section of your supermarket, and in Asian groceries.
Grilling Tip: Oil the grill rack just before cooking. The grill should already be heated and the coals or burners adjusted for the correct temperature. Oil a folded paper towel. Hold it with tongs and pull it toward you over the rack. Do not use cooking spray on a hot grill.