Marinate the Beef:
In a bowl, toss sliced beef with 1 tablespoon soy sauce and cornstarch. Set aside while prepping the rest.
Make the Sauce:
In a small bowl, whisk together remaining soy sauce, oyster sauce, hoisin sauce, brown sugar, garlic, and ginger. Set aside.
Cook the Broccoli:
Heat 1 tablespoon oil in a large skillet or wok over medium-high heat. Add broccoli and water; cover and steam for 2–3 minutes until just tender-crisp. Remove and set aside.
Sear the Beef:
Add remaining oil to the skillet. Add marinated beef in a single layer and sear for 2–3 minutes per side until browned and cooked through.
Combine Everything:
Return broccoli to the pan. Pour in the sauce and stir well to coat. Cook for another 1–2 minutes until the sauce thickens and everything is hot.
Serve:
Serve over steamed rice and garnish with sesame seeds and chopped green onions, if desired.