Begin by cooking the egg noodles according to package instructions. Drain and set aside.
In a large skillet or wok, heat the sesame oil over medium-high heat. Add the finely chopped onion and sauté until translucent, about 3-4 minutes.
Add the minced garlic and grated ginger, stirring for another 1-2 minutes until fragrant.
Increase the heat to high and add the ground beef, breaking it apart with a spatula. Cook until browned, about 5-7 minutes.
Stir in the sliced bell peppers and mushrooms, cooking until the vegetables are tender, about 4-5 minutes.
Drizzle the soy sauce, hoisin sauce, and sprinkle the chili flakes over the beef and vegetable mixture. Season with salt and pepper to taste, stirring to combine.
Carefully fold in the cooked egg noodles, mixing everything well to ensure the noodles are coated in the sauce.
Allow the mixture to cook for an additional 2-3 minutes on low heat, stirring occasionally, to allow the flavors to meld together.
Once ready, remove from heat and transfer to a serving dish.
Notes
Serve hot, garnished with chopped green onions and sesame seeds for added crunch and flavor.