Thinly slice the flank steak against the grain into bite-sized strips and season with sea salt and black pepper.
In a small bowl, whisk together the coconut aminos, toasted sesame oil, grated fresh ginger, minced garlic, and arrowroot starch until smooth.
Heat the avocado oil in a large skillet or wok over medium-high heat until shimmering.
Add the beef strips in a single layer and sear for 2-3 minutes until browned and caramelized, then remove from the pan.
Add the broccoli florets to the same pan with a splash of water, covering for 2 minutes to steam until bright green and tender-crisp.
Return the beef to the pan, pour the sauce over the mixture, and toss for 1 minute until the sauce thickens and coats everything beautifully.
Garnish with sesame seeds before serving.