Cook the egg noodles according to the package instructions. Drain and set aside.
In a large skillet or wok, heat vegetable oil over medium-high heat. Add diced onion and sauté for 2-3 minutes until softened.
Stir in the minced garlic and cook for an additional minute until fragrant.
Add the ground beef to the skillet, breaking it up with a spatula. Cook until browned, about 5-7 minutes.
In a small bowl, mix together the soy sauce, oyster sauce, brown sugar, cornstarch, and beef broth. Pour this mixture over the cooked beef.
Stir in the sliced bell pepper and julienned carrots. Cook for an additional 5 minutes until the vegetables are tender.
Add the cooked noodles to the skillet and toss everything together until well combined. Cook for another 2-3 minutes, allowing the noodles to absorb the flavors.
Season with salt and pepper to taste.
Serve hot, garnished with sliced green onions.