To make the bulgogi sauce, in a small bowl, combine all the ingredients. Mix until thoroughly combined and set aside.
Bring a pot of water to a boil. Once boiling, cook the noodles according to the package instructions. Once they are cooked through, take them out and set aside.
In a large wok or pan, heat the oil over medium heat. Once it gets nice and hot, add the white parts of the green onions and cook for 30 seconds or until fragrant. Increase the heat to medium-high, add the beef, and cook for 2 to 3 minutes or until the beef is halfway cooked.
Add the onion, mushrooms, and carrot. Stir-fry for 1 to 2 minutes or until the vegetables are slightly cooked. Increase the heat to high, add the drained noodles, sauce, and dark soy sauce (if using). Toss together for 2 to 3 minutes or until the noodles are thoroughly coated with the sauce. Turn the heat off.
Add the garlic chives and sesame oil. Give a final mix.
Divide the noodles evenly between two serving plates. Top with the green parts of the green onions and sesame seeds. Serve and enjoy immediately.
