Slice the beef thinly.
Julienne the onion and bell pepper.
In a bowl, mix soy sauce, sugar, minced garlic, sesame oil, and pepper to make the marinade.
Marinate the beef and vegetables in the sauce for 10 minutes.
Heat cooking oil in a pan and stir-fry the marinated beef and vegetables.
Toast the bread slices in a toaster.
Place the cooked bulgogi on top of the toasted bread.
Add lettuce as desired.