Slice your flank steak or sirloin thinly against the grain. Place the beef in a bowl and add soy sauce, minced garlic, and grated ginger. Marinate for 15-20 minutes.

Heat a large skillet or wok over high heat. Add a drizzle of oil, then add the marinated beef strips in a single layer. Sear for 2-3 minutes until browned but slightly pink.

Transfer the beef to a plate and cover. In the same skillet, add mixed vegetables and stir-fry for 3-4 minutes until tender-crisp.

Return the cooked beef to the skillet. Sprinkle cornstarch and stir to combine. Cook for another 2-3 minutes until the sauce thickens.

Remove from heat and serve immediately over steamed rice or noodles, garnished with sesame seeds or green onions.