Thicken Sauce: Add the cornstarch slurry to the skillet and cook for 1-2 minutes, stirring constantly, until the sauce thickens.
Add Noodles: Add the cooked lo mein noodles or spaghetti and toss everything together until well coated.
Garnish and Serve: Garnish with chopped green onions and sesame seeds, if desired. Serve hot.
