Thinly slice onion and bell pepper.
Season beef for bulgogi with soy sauce, minced garlic, sugar, and sesame oil.
Add oil to a pan and stir-fry the beef.
When the beef is half cooked, add onion and bell pepper and stir-fry together.
Cut pita bread in half and open up the inside.
Fill pita bread with stir-fried bulgogi and vegetables.
Optionally, add lettuce, tomato, and yogurt sauce.