Bring a large pot of salted water to a boil. Cook the lo mein noodles (or spaghetti) until al dente according to package directions. Drain, rinse briefly under warm water, and toss with 1/2 tsp sesame oil to keep them from sticking. Set aside.

Slice the beef sirloin very thin against the grain; pat dry and season lightly with salt and pepper.

In a small bowl, whisk together 3 tbsp soy sauce, 2 tbsp oyster sauce, and 1 tbsp hoisin sauce. Add a tablespoon of water if you prefer a looser sauce. Set aside.

Heat a large skillet or wok over high heat. Add 1 tbsp vegetable oil and swirl to coat. Add half the beef in a single layer and sear 1–2 minutes per side until browned but not fully cooked through. Remove to a plate and repeat with the remaining beef.

Reduce heat slightly, add the remaining 1 tbsp vegetable oil. Add minced garlic and ginger; stir 20–30 seconds until fragrant.

Add sliced carrots and stir-fry 1–2 minutes, then add broccoli florets and 2–3 tablespoons water to create a little steam; cover briefly if needed to tenderize the broccoli.

Stir in the green peas and cook 30–60 seconds more until heated through. Return the beef to the pan.

Add cooked noodles and the sauce. Toss or stir-fry 1–2 minutes until everything is evenly coated and the beef finishes cooking.

Turn off the heat. Drizzle 1 tsp sesame oil over the top and sprinkle with sesame seeds if using. Serve immediately.