Mix all marinade ingredients together.
Add the sliced beef, green onion, onion, and carrot to the marinade. Mix thoroughly, making sure that the meat is marinated on each side. Let marinade for 4 hours, preferably overnight.
When ready to use, let meat sit out at room temp for 30 minutes.
In a large skillet or wok over high heat, add 2 tbsp of cooking oil. Add the mushrooms and beef bulgogi. Stir fry for 4-5 minutes.
Turn off the heat. Drizzle 1 tbsp of sesame oil over the beef and mix.
Serve the beef bulgogi stir fry over steamed rice. Garnish with more toasted sesame seeds.