In a bowl, mix sliced beef with soy sauce, cornstarch, and baking soda if using. Let sit for at least 10 minutes while prepping other ingredients.
In a small bowl, whisk together soy sauce, oyster sauce, hoisin, brown sugar, sesame oil, and the cornstarch slurry. Set aside.
Heat 1 tablespoon of oil in a large skillet or wok over medium-high heat. Add broccoli and stir fry for 2–3 minutes until bright green and just tender. Remove from pan and set aside.
Add the remaining oil to the pan. Sear the beef in batches until browned and just cooked through. Avoid overcrowding the pan.
Return all the beef to the pan, add the garlic and ginger, and stir for 30 seconds. Add the broccoli and pour in the sauce. Toss everything together and cook until the sauce thickens and coats the meat and veggies, about 2–3 minutes.
Serve hot over steamed rice or noodles. Garnish with sesame seeds or sliced green onions if desired.