Slice the flank steak against the grain into thin, bite-sized strips.
In a small bowl, whisk together coconut aminos, arrowroot powder, minced ginger, and minced garlic to create the stir-fry sauce.
Heat sesame oil in a large skillet or wok over medium-high heat until shimmering.
Add the beef strips to the pan, season with salt and pepper, and sear until browned, about 2-3 minutes.
Remove the beef from the pan and set it aside on a plate.
Add broccoli florets to the same pan with a splash of water, cover with a lid, and steam for 3 minutes until tender-crisp.
Return the beef to the pan and pour the prepared sauce over the mixture.
Toss everything together for 1-2 minutes until the sauce thickens and beautifully coats the beef and broccoli.
Garnish with sesame seeds and serve immediately while hot.