Whisk the coconut aminos, water, arrowroot powder, minced ginger, and minced garlic in a small bowl to create the sauce.
Season the thinly sliced flank steak with sea salt and black pepper on both sides.
Heat the toasted sesame oil in a large skillet or wok over medium-high heat until shimmering.
Add the beef to the hot pan in a single layer and sear until browned, approximately 2 minutes per side, then remove and set aside.
Add the broccoli florets to the same pan with a splash of water, covering with a lid for 2 minutes to steam until tender-crisp.
Return the beef to the pan and pour the sauce mixture over the ingredients, tossing constantly until the glaze thickens and coats everything.
Garnish the stir-fry with sesame seeds and serve immediately while hot.