Add the cornstarch slurry to the skillet and cook for 1-2 minutes, stirring constantly, until the sauce has thickened.
Add the cooked lo mein noodles or spaghetti to the skillet and toss everything together until the noodles are fully coated with the sauce.
Garnish with chopped green onions and sesame seeds, if desired.
Serve the Beef Lo Mein hot.
Servings: 4