Slice flank steak thinly against the grain, mince garlic and ginger, and prepare all vegetables. Set aside.

Bring a large pot of salted water to a rolling boil. Cook lo mein noodles 4–5 minutes until tender-chewy, drain in a colander, and toss with a splash of oil to prevent sticking.

In a small bowl whisk together soy sauce, oyster sauce, sesame oil, beef broth, cornstarch, and water until the cornstarch is fully dissolved. Keep the sauce near the stove.

Heat a wok over high heat for about 2 minutes until smoking hot. Add 1½ tablespoons vegetable oil and swirl to coat.

Add half the beef in a single layer; sear 60–90 seconds per side until browned. Remove to a plate and repeat with remaining beef.

Add remaining 1½ tablespoons oil to the wok. Stir-fry broccoli florets and carrot matchsticks for 3–4 minutes until beginning to soften.

Push vegetables to the side, add garlic and ginger to the center, and toast 30 seconds until fragrant. Add bell pepper strips and green onions; cook 2 minutes, stirring constantly.

Return cooked noodles and seared beef to the wok. Pour sauce over everything and toss continuously for 2–3 minutes until the sauce thickens and coats all ingredients.

Serve immediately while hot, garnished with extra green onions or sesame seeds if desired.