Cook the lo mein noodles according to the package directions. Drain and set aside.
Heat the vegetable oil in a large skillet or wok over medium-high heat. Add the beef and cook for 5 to 7 minutes, stirring occasionally, until browned and cooked through. Transfer it to a plate.
Add the broccoli and sliced onion to the same skillet. Cook for 3 to 4 minutes, stirring often, until they begin to soften.
Stir in the garlic and cook for about 1 minute.
Whisk together the soy sauce, oyster sauce, hoisin sauce, brown sugar, rice vinegar, sesame oil, and ground ginger if using.
Put the beef back into the skillet and pour the sauce over it. Stir with the vegetables and cook for 2 to 3 minutes.
Add the cooked noodles and toss gently until the beef, broccoli, onion, and noodles are evenly mixed with the sauce.
Remove from the heat, sprinkle with chopped green onions, and serve hot.