Prepare the flank steak by slicing it very thinly against the grain into bite-sized strips.
In a small bowl, whisk together the tamari, grated fresh ginger, minced garlic, arrowroot powder, and water to create the stir-fry sauce.
Place the broccoli florets in a steamer basket over boiling water for 3 minutes until vibrant green and crisp-tender, then set aside.
Heat the toasted sesame oil in a large skillet or wok over medium-high heat.
Add the beef strips to the skillet in a single layer, seasoning with sea salt and black pepper.
Sear the beef for 2 minutes without moving it to develop a golden crust, then flip and cook for another 1 minute.
Add the steamed broccoli to the skillet with the beef.
Pour the prepared sauce over the mixture and toss constantly for 1 minute until the sauce thickens and coats everything evenly.
Remove from heat immediately and garnish with sesame seeds before serving.