Slice the beef thinly and marinate it in the seasoning sauce.
Julienne the onion, carrot, and green onion.
Heat some cooking oil in a pan and stir-fry the marinated beef.
Add the vegetables and stir-fry together.
Cut the bread in half and lightly toast both sides.
Place bulgogi, vegetables, and lettuce on the bread.
Cover with the other half of the bread to finish the sandwich.