Prepare the Ingredients

1. Cook the Noodles: Begin by cooking the lo mein noodles according to the package directions. Drain and set aside.
2. Prep the Beef: Slice the beef thinly against the grain. This ensures tenderness when cooking.
3. Prepare the Vegetables: Cut the broccoli into florets, thinly slice the onion, and if you’re using bell pepper, slice that too.

Make the Sauce

1. Mix the Sauce: In a small bowl, whisk together the soy sauce, oyster sauce, hoisin sauce, rice vinegar, brown sugar, sesame oil, cornstarch (if using), water, and black pepper. Set the sauce aside.

Cook the Beef and Vegetables

1. Stir-Fry the Beef: Heat 1 tablespoon of vegetable or sesame oil in a large skillet or wok over medium-high heat. Once hot, add the beef in a single layer and cook for about 2-3 minutes per side, or until browned and cooked through. Remove the beef from the skillet and set aside.
2. Stir-Fry the Vegetables: In the same skillet, add the garlic and onion. Stir-fry for about 1-2 minutes, until fragrant. Add the broccoli and bell pepper (if using), and stir-fry for 3-4 minutes, until the broccoli is bright green and tender-crisp.

Combine Everything

1. Add the Noodles and Beef: Add the cooked noodles and beef back to the skillet with the vegetables. Pour the prepared sauce over the top and toss everything together to combine, making sure the noodles and beef are evenly coated with the sauce.
2. Simmer: Let the dish simmer for 2-3 minutes to heat everything through and allow the sauce to thicken slightly.

Serve

1. Serve the Lo Mein: Plate the Beef and Broccoli Lo Mein and serve hot, garnished with sesame seeds or green onions if desired.