Slice the beef: Freeze the steak for 15 minutes to firm it up. Slice thinly against the grain. Aim for 1/8-inch slices so the beef sears quickly and stays tender.

Marinate: In a bowl, mix soy sauce, cornstarch, sesame oil, and black pepper. Toss in the beef until coated. Let it sit while you prep the vegetables.

Make the sauce: In a small bowl, whisk soy sauce, oyster sauce, hoisin (or sugar), rice vinegar, broth, cornstarch, and chili if using. Set aside.

Prep vegetables: Slice zucchini, onion, and mince the garlic and ginger. Keep everything nearby—stir-fries move fast.

Heat the pan: Place a large skillet or wok over medium-high heat. Add 1 tablespoon oil and swirl to coat until shimmering.

Sear the beef: Add beef in a single layer. Don’t crowd the pan. Sear 60–90 seconds per side until browned but not fully cooked. Do this in batches if needed. Transfer to a plate.

Cook the vegetables: Add the remaining tablespoon of oil. Toss in onion and zucchini with a pinch of salt. Stir-fry 3–4 minutes until the zucchini is crisp-tender and lightly browned.

Add aromatics: Add garlic and ginger. Stir for 30 seconds until fragrant—don’t let them burn.

Combine and sauce: Return the beef and any juices to the pan. Whisk the sauce again (the cornstarch settles). Pour it in and toss constantly for 1–2 minutes until glossy and thickened.

Finish: Turn off the heat. Stir in green onions. Taste and adjust with a splash of soy, vinegar, or chili for balance.

Serve: Spoon over hot rice or toss with noodles. Garnish with sesame seeds if you like.