Slice the flank steak against the grain into very thin strips and season evenly with sea salt and black pepper.
In a small glass bowl, whisk together the coconut aminos, minced fresh ginger, minced garlic, arrowroot powder, and water until smooth 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 hot pan in a single layer and sear without moving for 2 minutes to develop a golden crust, then flip and cook for 1 additional minute before removing the beef from the pan.
Add the broccoli florets to the same pan with a tiny splash of water, cover with a lid, and steam for 2-3 minutes until they are bright green and tender-crisp.
Return the beef to the pan and pour the prepared sauce over the mixture, tossing constantly for 1 minute until the glaze thickens and coats every piece beautifully.
Transfer to a plate and garnish with toasted sesame seeds before serving immediately.