Heat gas or charcoal grill. Process beans in food processor, or mash in large bowl with fork until smooth. Add bread crumbs, Worcestershire sauce, onions and egg white; process with on/off pulses, or stir until well mixed.
Place sesame seed on plate. With wet hands, shape mixture into 6 flat oval-shaped patties, about 1/2 inch thick. Coat patties evenly on both sides with seed.
Place patties on grill over medium-high heat. Cover grill; cook 12 to 16 minutes, turning once, until patties are lightly browned on both sides and seed is toasted.
If desired, just before patties are done, place slices of bread on grill to toast lightly.
To serve, spread 1 side of each toasted slice of bread with 1 teaspoon guacamole. Top 6 slices of bread, guacamole side up, with patties. Top each with carrot. Cover with remaining bread slices, guacamole side down.