Slice the flank steak against the grain into thin strips and season evenly with sea salt and black pepper.
In a small bowl, whisk together the coconut aminos, minced ginger, minced garlic, arrowroot powder, and water to create the stir-fry sauce.
Heat the toasted sesame oil in a large skillet or wok over medium-high heat until it begins to shimmer.
Add the beef strips to the skillet in a single layer and sear until browned, approximately 2 minutes per side, then remove the beef from the pan and set aside.
Add the broccoli florets to the same skillet with a small splash of water, covering with a lid for 2 minutes to steam-sauté until they are bright green and tender-crisp.
Return the beef to the pan and pour the prepared sauce over the mixture, stirring constantly for 1 minute until the sauce thickens and becomes glossy.
Remove from heat, garnish with thinly sliced green onions, and serve immediately.