Marinate the beef: In a bowl, combine soy sauce, oyster sauce, and cornstarch. Mix well and then add the sliced beef. Let it marinate for 15 minutes to enhance the flavor.
Heat the pan: Heat vegetable oil in a wok or large skillet over medium-high heat. Ensure the oil is hot enough before proceeding to the next step.
Cook the aromatics: Add minced garlic and ginger to the pan and stir-fry for about 30 seconds, or until fragrant.
Brown the beef: Add the marinated beef to the skillet. Stir-fry for 3-4 minutes until all sides are browned and the beef is nearly cooked through.
Add the vegetables: Toss in the mixed vegetables, stir-frying for an additional 3-5 minutes until they are tender-crisp.
Season: Taste and season with salt and pepper as needed, adjusting according to your preference.
Serve: Serve hot over rice or noodles of your choice for a complete meal.
Notes
Fresh vegetables provide better texture and flavor. Avoid overcrowding the pan during cooking.