Slice the flank steak into thin strips against the grain to ensure every bite is tender and easy to chew.
In a small bowl, whisk together the coconut aminos, arrowroot powder, minced ginger, and minced garlic to create a smooth stir-fry sauce.
Heat the sesame oil in a large skillet or wok over medium-high heat until it begins to shimmer.
Add the beef strips to the pan in a single layer, seasoning with sea salt and black pepper, then sear for 2 minutes until deeply browned.
Toss in the broccoli florets and a tablespoon of water, then cover with a lid for 2 minutes to lightly steam the vegetables until bright green.
Remove the lid, pour the prepared sauce over the beef and broccoli, and stir constantly for 1 minute until the glaze thickens and coats every piece.
Transfer the stir-fry to a plate and sprinkle with sesame seeds for a nutty crunch before serving immediately.