Velvet the beef by tossing with baking soda for 15 minutes, then rinse thoroughly and pat dry.
Whisk all sauce ingredients together in a small bowl and set aside.
Stir-fry broccoli in 1 tbsp hot oil over high heat for 2 to 3 minutes until bright and just tender. Remove and set aside.
Sear beef in remaining oil over high heat in a single layer for 1 minute, then stir-fry 1 to 2 minutes more.
Add garlic and ginger on medium heat, stir 30 seconds until fragrant.
Pour sauce into the pan and simmer 1 to 2 minutes until thick and glossy.
Return broccoli to the pan, toss to coat, and serve immediately over rice with sesame seeds and green onions.