Return the cooked beef to the skillet with the vegetables.
Add the cooked noodles to the skillet and toss to combine.
Make the Sauce:
In a small bowl, mix together the soy sauce, oyster sauce, sesame oil, and beef broth.
Pour the sauce over the beef, vegetables, and noodles, stirring to coat everything evenly.
Add the cornstarch slurry to the skillet and stir continuously until the sauce thickens, about 2-3 minutes.
Serving:
Serve the beef lo mein hot, garnished with chopped green onions and sesame seeds if desired
