Prepare the sauce by whisking coconut aminos, rice vinegar, toasted sesame oil, and arrowroot powder in a small bowl until smooth.
Slice the flank steak against the grain into thin, bite-sized strips and season with sea salt and black pepper.
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, then remove from the pan and set aside.
In the same pan, add the broccoli florets with a splash of water, cover, and steam for 2 minutes until bright green and tender-crisp.
Stir in the minced garlic and grated ginger, sautéing for 30 seconds until fragrant.
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 everything.
Garnish with sesame seeds and serve immediately.