Toss sliced steak with baking soda in a medium bowl and let sit for 10 minutes to tenderize.
Rinse the beef thoroughly under cold water to remove baking soda, then pat dry with paper towels and season lightly with salt and pepper.
Heat olive oil in a large skillet or wok over medium-high heat.
Add the beef in a single layer and sear for 2–3 minutes per side until browned and just cooked through, then remove from the skillet and set aside.
In the same skillet, add broccoli and a splash of water; cover and steam for 2–3 minutes until just tender.
Return the cooked beef to the skillet and toss to combine.
In a small bowl, whisk together all the sauce ingredients until smooth.
Pour the sauce into the skillet and cook, stirring, for 2-5 minutes or until thickened and glossy and garlic is fragrant.
Stir in green onions until coated in sauce.
Top with sesame seeds if desired, remove from heat and serve.