Thinly slice the flank steak against the grain into bite-sized strips.
In a small bowl, whisk together tamari, toasted sesame oil, rice vinegar, honey, and arrowroot powder to create the stir-fry sauce.
Heat avocado oil in a large skillet or wok over medium-high heat until shimmering.
Add the beef strips in a single layer, seasoning with sea salt and black pepper, and sear until browned, about 2-3 minutes.
Remove the beef from the pan and set aside; add the broccoli florets and a splash of water, covering for 2 minutes to steam-tenderize.
Stir in the minced garlic and grated ginger, sautéing for 1 minute until fragrant.
Return the beef to the pan and pour the sauce over the mixture, tossing constantly until the glaze thickens and coats everything beautifully.
Garnish with sesame seeds before serving.