Bring a large pot of water to a boil over high heat. Once boiling, add 8 ounces of noodles, stirring occasionally. Cook according to package instructions, usually around 5–7 minutes, until al dente. Drain the noodles in a colander and set them aside, letting any excess water drip off while you prepare the beef.

In a mixing bowl, coat the sliced flank steak with 2 tablespoons of cornstarch, ensuring each piece is evenly covered. Allow it to sit for about 10 minutes at room temperature.

Heat 2 tablespoons of vegetable oil in a large skillet or wok over medium-high heat. Once hot, add the beef in batches, ensuring not to overcrowd the skillet. Sauté for about 3-4 minutes until the beef is browned and just cooked through, then remove it from the skillet and set it aside.

In the same skillet, add the minced garlic and ginger, stirring for about 30 seconds until fragrant. Next, add the julienned carrot and sliced bell pepper, continuing to stir-fry for approximately 3-4 minutes.

In a small bowl, whisk together 3 tablespoons of soy sauce, 2 tablespoons of hoisin sauce, 1 tablespoon of brown sugar, 1 tablespoon of rice vinegar, and 1 teaspoon of sesame oil until fully combined.

Return the cooked beef to the skillet with the sautéed vegetables. Pour the sauce over the mixture, tossing everything together to ensure each piece is well coated. Cook for an additional 2 minutes.

Now, gently add the cooked noodles to the skillet with the beef and vegetables. Using tongs or a spatula, carefully toss everything together until the noodles are well coated with the sauce and flavors.

Transfer your vibrant Mongolian Beef Noodles to a serving platter. To finish, sprinkle some chopped green onions on top for added flavor and presentation.