Cook the egg noodles according to package instructions. Drain and set aside.

In a large skillet or wok, heat the vegetable oil over medium-high heat. Add the sliced flank steak and season with salt and pepper. Stir-fry for about 3-4 minutes until browned and cooked through. Remove the beef from the skillet and set aside.

In the same skillet, add the bell pepper, snap peas, green onions, garlic, and ginger. Stir-fry for about 3-4 minutes until the vegetables are tender-crisp.

Return the cooked beef to the skillet. Add the hoisin sauce, soy sauce, sesame oil, and red pepper flakes (if using). Stir everything together and cook for an additional 2 minutes to heat through.

Add the cooked egg noodles to the skillet and toss everything together until the noodles are well coated with the sauce. Cook for another minute to warm the noodles.

Serve hot, garnished with additional green onions if desired.