Heat the oil: In a large skillet or wok, heat the vegetable oil over medium-high heat until shimmering.
Cook the beef: Add the sliced beef, making sure it’s in a single layer. Stir-fry until browned and cooked through, about 3-5 minutes. Remove the beef from the skillet and set aside.
Sauté aromatics: In the same skillet, add the minced garlic and grated ginger, sautéing for about 30 seconds until fragrant.
Add vegetables: Toss in the mixed vegetables. Stir-fry for about 4-5 minutes until tender-crisp.
Combine ingredients: Return the cooked beef to the skillet, then add soy sauce and oyster sauce. Stir to combine all ingredients well.
Heat through: Cook for an additional 2 minutes until everything is heated through, and the sauce coats the beef and veggies evenly.
Season and serve: Season with salt and pepper to taste. Serve hot over cooked rice or noodles.
Notes
Slice the beef thinly against the grain for maximum tenderness. Cooking on high heat helps to sear the beef and keep the vegetables crisp.