Start by cooking the noodles according to the package instructions. Drain and set aside.
In a large skillet or wok, heat the vegetable oil over medium-high heat.
Add the chopped onion and minced garlic. Sauté for about 2 minutes until fragrant.
Add the ground beef to the skillet, breaking it apart with a spoon. Cook for about 5-6 minutes, or until browned and cooked through.
Stir in the sliced bell peppers, broccoli florets, and julienned carrots. Cook for an additional 3-4 minutes until the vegetables are tender-crisp.
Add the drained noodles along with the soy sauce, oyster sauce (if using), minced ginger, and black pepper. Toss everything together until evenly combined and heated through, about 2 minutes.
Remove from heat and serve hot, garnished with sliced green onions and sesame seeds if desired.