Slice the flank steak against the grain into thin, bite-sized strips to ensure maximum tenderness.
In a small bowl, whisk together the tamari, water, arrowroot powder, and toasted sesame oil to create the stir-fry sauce.
Heat the extra virgin olive 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.
In the same pan, add the broccoli florets, minced garlic, grated ginger, and red pepper flakes with a splash of water, covering for 2 minutes to steam-soften.
Return the beef to the pan and pour the prepared sauce over the mixture, tossing constantly for 1 minute until the sauce thickens and coats everything beautifully.
Garnish with sesame seeds and serve immediately while hot and fragrant.