Prepare the beef: Pat the beef slices dry with paper towels to remove excess moisture (this helps with browning). Place them in a bowl and add soy sauce, oyster sauce, hoisin sauce, cornstarch, and sesame oil. Mix well so the beef is fully coated, then cover and let marinate for at least 15 minutes.

Preheat the pan: Heat a wok or large skillet over medium-high heat until hot. Add 1 tablespoon of vegetable oil and swirl to coat the surface. Once the oil is shimmering, add the beef in a single layer (do this in batches if needed). Cook for about 2 minutes on each side until browned but not fully cooked through. Remove the beef from the pan and set aside on a plate.

Cook the aromatics: Add the remaining tablespoon of oil to the same pan. Toss in the onion, garlic, and ginger. Stir-fry for about 1–2 minutes until fragrant, making sure the garlic doesn’t burn.

Stir-fry the vegetables: Add the bell pepper, broccoli, carrot, and zucchini. Stir constantly for 3–4 minutes, until the vegetables are tender-crisp but still vibrant in color. You can splash a little broth into the pan to create steam and soften the veggies faster.

Combine beef and sauce: Return the beef to the pan along with any juices from the plate. Pour in the remaining broth and stir everything together. Cook for 2–3 more minutes until the beef is fully cooked, the sauce has thickened slightly, and everything is coated evenly.

Finish with flavor: Add a splash of rice vinegar or lime juice to brighten the dish. Toss well, then remove from heat.

Serve: Transfer the stir fry to a serving platter or individual bowls. Garnish with sesame seeds and sliced green onions for a fresh crunch.