- Combine onion and soy sauce in a medium-size bowl; let stand 5 minutes.
- Add beef, bread and egg and thoroughly mix together. Shape mixture into four patties; place on rack of broiler pan.
- Broil patties 4 inches from heat source 4 to 5 minutes on each side, to at least medium doneness (160ºF.).
- Remove patties from pan and brush tops generously with hoisin sauce.