In a large bowl, combine the water chestnuts, teriyaki sauce, onions, salt and pepper. Crumble beef over mixture and mix just until combined. Shape into seven 1/2-in.-thick patties.
Prepare the grill for indirect heat. Grill, covered, over indirect medium heat for 6-8 minutes on each side or until meat is no longer pink and a thermometer reads 160°. Serve on buns with tomato and lettuce.