Creating a delicious Beef and Tomato Stir Fry is easy if you follow these simple steps:

1. Preparation: Start by slicing the beef sirloin into thin strips. Ensure the slices are uniform for even cooking.

2. Marinate Beef: In a bowl, combine the sliced beef with 1 tablespoon of soy sauce, 1 tablespoon of cornstarch, a pinch of salt, and pepper. Mix well and let it marinate for about 10 minutes.

3. Heat Oil: In a large skillet or wok, heat 2 tablespoons of vegetable oil over medium-high heat until shimmering.

4. Cook Beef: Add the marinated beef to the pan in a single layer. Sear for about 2-3 minutes until browned. Stir occasionally.

5. Add Aromatics: Once the beef is browned, add the minced garlic and ginger. Stir-fry for another 30 seconds until fragrant.

6. Incorporate Vegetables: Add the sliced onions and diced tomatoes to the pan. Stir well to combine.

7. Add Sauces: Pour in the remaining soy sauce and the oyster sauce. Toss everything together, ensuring the beef and vegetables are well coated.

8. Simmer: Cook for an additional 3-5 minutes until the tomatoes break down slightly and create a sauce.

9. Adjust Seasoning: Taste and adjust the seasoning with more salt and pepper if necessary.

10. Serve: Remove from heat and garnish with chopped green onions before serving.

These straightforward steps will guide you in creating a tantalizing Beef and Tomato Stir Fry that your whole family will enjoy.