Heat 1 tbsp oil in a large skillet or wok over medium-high heat.
Add beef and stir-fry 2–3 minutes until browned. Remove and set aside.
Add remaining oil, garlic, ginger, and broccoli. Stir-fry 3–4 minutes until broccoli is tender-crisp.
In a small bowl, whisk coconut aminos, vinegar, sesame oil, and sweetener.
Return beef to the pan, pour sauce over, and stir to coat.
Simmer 1–2 minutes. Sprinkle xanthan gum if thicker sauce is desired.
Garnish with sesame seeds and serve hot.