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 tamari, rice vinegar, arrowroot powder, and red pepper flakes until smooth.
Heat the avocado oil in a large skillet or wok over high heat until shimmering.
Add the beef in a single layer and sear for 2 minutes until browned and caramelized, then remove from the pan and set aside.
In the same pan, add the broccoli florets with a splash of water, covering for 2 minutes to steam-sauté until vibrant green and tender-crisp.
Stir in the minced garlic and grated ginger, cooking for 30 seconds until fragrant.
Return the beef to the pan, pour in the sauce mixture, and toss constantly for 1 minute until the glaze thickens and coats everything.
Remove from heat, drizzle with toasted sesame oil, and garnish with sesame seeds before serving.