Slice the flank steak against the grain into thin, bite-sized strips to ensure maximum tenderness.
In a small glass bowl, whisk together the coconut aminos, arrowroot powder, minced garlic, grated ginger, and one tablespoon of the water until smooth.
Heat the toasted sesame oil in a large stainless steel skillet or wok over medium-high heat until shimmering.
Add the beef strips to the hot pan in a single layer, seasoning with sea salt and black pepper, and sear for 2-3 minutes until beautifully browned.
Toss in the broccoli florets along with the remaining tablespoon of water, then cover the pan with a lid for 2 minutes to lightly steam the vegetables until crisp-tender.
Remove the lid and pour the prepared sauce over the beef and broccoli, stirring constantly for 1 minute as the sauce thickens into a glossy, savory glaze.
Transfer the stir-fry to a plate and sprinkle with sesame seeds for a final touch of crunch and nutty flavor.