Ingredients:

For the Beef:
1 lb beef sirloin, thinly sliced
2 tablespoons soy sauce
1 tablespoon cornstarch
1 tablespoon vegetable oil
For the Lo Mein:
8 oz lo mein noodles or spaghetti
2 tablespoons vegetable oil
1 onion, thinly sliced
2 cloves garlic, minced
1 cup sliced carrots
1 cup sliced bell peppers (red, green, or yellow)
1 cup broccoli florets
1 cup snow peas
1/4 cup soy sauce
2 tablespoons oyster sauce
1 teaspoon sesame oil
1/4 cup beef broth
1 tablespoon cornstarch mixed with 1 tablespoon water (slurry)
Green onions, chopped (for garnish)
Sesame seeds (optional, for garnish)

Instructions:

Preparing the Beef:
Marinate the Beef:
In a bowl, combine the soy sauce and cornstarch.
Add the thinly sliced beef and toss to coat evenly.
Let the beef marinate for about 15 minutes.
Cook the Beef:
In a large skillet or wok, heat 1 tablespoon of vegetable oil over medium-high heat.
Add the marinated beef and stir-fry until browned and cooked through, about 5-7 minutes.
Remove the beef from the skillet and set aside.
Preparing the Lo Mein:
Cook the Noodles:
Cook the lo mein noodles or spaghetti according to package instructions. Drain and set aside.
Sauté the Vegetables:
In the same skillet or wok, add the remaining 2 tablespoons of vegetable oil.
Add the sliced onion and minced garlic, and sauté until fragrant, about 1-2 minutes.
Add the sliced carrots, bell peppers, broccoli florets, and snow peas. Stir-fry for about 5 minutes until the vegetables are tender-crisp.
Combine Ingredients:
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.