Cook noodles according to package instructions. Drain and set aside.
In a small bowl, mix soy sauce, hoisin sauce, brown sugar, oyster sauce (if using), water, and cornstarch. Stir until well combined. Set sauce aside.
Heat sesame oil in a large skillet or wok over medium-high heat.
Add sliced onion and cook until softened, about 2 minutes.
Add ground beef and cook until browned, breaking it apart with a spoon. Drain excess grease if needed.
Stir in minced garlic and grated ginger, cooking for another 1-2 minutes until fragrant.
Add shredded carrots and cook for 2 minutes.
Pour in the prepared sauce, stirring to coat the beef and veggies evenly.
Toss in the cooked noodles, mixing well to ensure everything is coated with the sauce.
Add chopped green onions and red pepper flakes if desired.
Cook for another 1-2 minutes until heated through.
Garnish with sesame seeds and serve hot!