Slice the flank steak against the grain into thin strips and season with sea salt and black pepper.
In a small bowl, whisk together the coconut aminos, toasted sesame oil, 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 in a single layer and sear for 2 minutes until browned, then remove from the pan and set aside.
Add the broccoli florets and a splash of water to the pan, covering for 2 minutes to steam until bright green and tender-crisp.
Stir in the minced garlic, grated ginger, and red pepper flakes, sautéing for 30 seconds until fragrant.
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.
Garnish with sesame seeds before serving hot.