Creating Beef & Onion Stir-Fry is simple if you follow these steps:

1. Prepare the Marinade: In a bowl, combine soy sauce, oyster sauce, cornstarch, minced garlic, and ginger. Mix well.
2. Marinate the Beef: Add the sliced beef to the marinade and let it sit for about 10 minutes to absorb the flavors.
3. Heat the Oil: In a large pan or wok, heat the vegetable oil over medium-high heat until shimmering.
4. Cook the Beef: Add the marinated beef to the pan in a single layer, allowing it to sear for about 2-3 minutes. Flip the beef to brown all sides. Remove it from the pan and set aside.
5. Cook the Onions: In the same pan, add the sliced onions, sautéing for about 5 minutes until they turn golden and caramelized.
6. Combine Ingredients: Once the onions are ready, return the beef to the pan, mixing everything together. Cook for an additional 2-3 minutes, allowing the flavors to meld.
7. Season: Taste and season with salt and pepper, adjusting to your preference.
8. Garnish: Remove from heat and garnish with chopped green onions.
9. Serve: Serve hot over cooked rice or noodles for a complete meal.

These straightforward steps will guide you in creating a wonderful Beef & Onion Stir-Fry that is sure to delight!