In a small bowl, whisk together the coconut aminos, water, and arrowroot powder until smooth to create the stir-fry base.
Slice the flank steak against the grain into thin, bite-sized strips and season evenly with sea salt and black pepper.
Heat the toasted sesame oil in a large skillet or wok over medium-high heat until shimmering.
Add the beef strips in a single layer and sear for 2 minutes until browned, then remove from the pan and set aside.
Add the broccoli florets to the same pan with an extra splash of water, covering for 2 minutes to steam until tender-crisp.
Stir in the minced garlic and grated ginger, cooking for 30 seconds until highly fragrant.
Return the beef to the pan and pour the sauce mixture over the ingredients, tossing constantly for 1 minute until the sauce thickens.
Garnish with sesame seeds and serve immediately while hot.