Begin by gathering all your ingredients and slice the beef flank steak thinly against the grain into strips. Prepare the mixed vegetables, mince the garlic, and grate the ginger.

In a medium bowl, add the sliced beef along with soy sauce, hoisin sauce, and optional cornstarch. Toss together until well coated and let marinate for about 10 minutes.

Bring a large pot of water to boil and cook the noodles according to package instructions, usually about 4-6 minutes until al dente. Drain and toss with a drizzle of sesame oil.

Heat a large skillet or wok over high heat and add 2 tablespoons of vegetable oil. Once hot, add the marinated beef in a single layer. Sear for about 2-3 minutes until browned.

In the same skillet, add more oil if needed, then add the mixed vegetables, garlic, and ginger. Stir-fry for approximately 3-4 minutes until vibrant and just tender.

Return the cooked beef to the skillet with the vegetables, add the cooked noodles, and toss everything together. Adjust seasoning with salt and pepper.

Serve the stir fry hot, garnished with sliced green onions and sesame seeds. Enjoy your meal immediately!