Marinate the Beef:

In a bowl, toss the sliced beef with soy sauce, cornstarch, sesame oil, and black pepper. Let it marinate for 10-15 minutes while preparing the other ingredients.

Cook the Noodles:

Boil the noodles according to package instructions. Drain and set aside.

Make the Sauce:

In a small bowl, whisk together soy sauce, hoisin sauce, oyster sauce, brown sugar, rice vinegar, chili flakes (if using), ginger, and garlic. Set aside.

Stir-Fry the Beef:

Heat 1 tablespoon of vegetable oil in a large skillet or wok over medium-high heat.

Add the marinated beef and cook for 2-3 minutes until browned. Remove and set aside.

Cook the Vegetables:

In the same skillet, add the remaining 1 tablespoon of oil.

Stir-fry the onion, bell pepper, and snap peas (or broccoli) for 3-4 minutes until tender-crisp.

Combine Everything:

Return the beef to the skillet.

Pour in the prepared sauce and bring to a simmer. Let it thicken slightly for 1-2 minutes.

Toss in the cooked noodles and mix well to coat everything in the sticky sauce.

Serve & Garnish:

Remove from heat and garnish with chopped green onions and sesame seeds.

Serve immediately and enjoy!