Prepare the Steak:
In a bowl, whisk soy sauce, oyster sauce, ginger, garlic, and sesame oil. Toss beef strips in the marinade and let sit for 10–15 minutes.
Cook the Onions:
Heat oil in a skillet over medium heat. Add sliced onions and sauté until soft and slightly caramelized. Season and set aside.
Sear the Beef:
Heat oil in the same pan over high heat. Add marinated beef and stir-fry for 2–3 minutes until browned.
Make the Sauce:
In a small bowl, whisk soy sauce, hoisin sauce, rice vinegar, and cornstarch.
Combine & Finish:
Pour sauce over the beef and simmer until thickened. Add onions back and stir well.
Serve your Chinese Pepper Steak with Onions hot over rice or noodles.