In a medium bowl, combine the sliced flank steak, 2 tablespoons of soy sauce, and cornstarch. Mix well to coat the beef and let it marinate for about 15 minutes.
While the beef is marinating, prepare the broccoli by blanching it in boiling water for 2 minutes until vibrant green and slightly tender. Drain and set aside.
In a large skillet or wok over medium-high heat, add 1 tablespoon of vegetable oil. Once hot, add the marinated beef in batches, making sure not to overcrowd the pan. Cook for about 2-3 minutes until browned and cooked through. Remove the beef from the skillet and set aside.
In the same skillet, add the remaining tablespoon of vegetable oil, garlic, and ginger. Sauté for about 30 seconds until fragrant.
Add the blanched broccoli and stir-fry for another 2 minutes.
Return the beef to the skillet, and add the oyster sauce, remaining soy sauce, and sesame oil. Stir everything together until the sauce thickens slightly and coats the beef and broccoli.
Season with salt and pepper to taste.
Serve the beef and broccoli over cooked rice or quinoa, garnished with sesame seeds if desired.
Notes
Serve with cooked rice or quinoa and garnish with sesame seeds if desired.