Slice the flank steak against the grain into very thin strips and season with sea salt and black pepper.
In a small bowl, whisk together the coconut aminos, minced ginger, minced garlic, red pepper flakes, 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 1-2 minutes per side until browned and caramelized, then remove the beef from the pan and set aside.
Add the broccoli florets to the same pan with a tablespoon of water, cover with a lid for 2 minutes to steam until tender-crisp and bright green.
Return the beef to the pan and pour the prepared sauce over the mixture.
Toss everything together for 1 minute until the sauce thickens and coats the beef and broccoli evenly.
Remove from heat, drizzle with toasted sesame oil, and garnish with sesame seeds before serving.