Slice the flank steak against the grain into thin, bite-sized strips to ensure maximum tenderness.
In a small bowl, whisk together the coconut aminos, water, arrowroot powder, minced ginger, and minced garlic to create the stir-fry sauce.
Heat the toasted sesame oil in a large skillet or wok over medium-high heat until shimmering.
Add the beef strips to the pan in a single layer, seasoning with sea salt and black pepper, and sear for 2-3 minutes until browned.
Remove the beef from the pan and set aside; add the broccoli florets and a splash of water to the same pan, covering with a lid for 2 minutes to steam until bright green.
Return the beef to the pan and pour the prepared sauce over the mixture, tossing constantly for 1 minute until the sauce thickens and glazes the ingredients.
Garnish the dish with sesame seeds and serve immediately while hot.