Slice the flank steak against the grain into thin, bite-sized strips and season with sea salt and black pepper.
In a small bowl, whisk together the coconut aminos, toasted sesame oil, minced fresh ginger, minced garlic, and arrowroot powder to create the stir-fry sauce.
Heat the avocado oil in a large skillet or wok over medium-high heat until shimmering.
Add the beef strips to the skillet in a single layer and sear for 2-3 minutes until browned and cooked through, then remove the beef from the pan and set aside.
Add the broccoli florets to the same pan with a splash of water, cover with a lid for 2 minutes to steam until bright green and tender-crisp.
Return the beef to the pan and pour the sauce over the mixture, tossing constantly for 1 minute until the sauce thickens and coats everything evenly.
Transfer to a plate and garnish with sesame seeds before serving.