Slice the flank steak against the grain into thin, bite-sized strips and season with sea salt and black pepper.
In a small bowl, whisk together the tamari, sesame oil, and arrowroot powder until the powder is fully dissolved to create the stir-fry glaze.
Heat one teaspoon of avocado oil in a large skillet or wok over medium-high heat until shimmering.
Add the beef strips in a single layer and sear for 1-2 minutes per side until browned, then remove the beef from the pan and set aside.
Add the remaining teaspoon of avocado oil to the pan along with the broccoli florets and a splash of water, covering for 2 minutes to steam-cook the broccoli.
Remove the lid and add the minced garlic and grated fresh ginger, sautéing for 30 seconds until fragrant.
Return the beef to the pan and pour the tamari mixture over the ingredients.
Toss everything together for 1 minute until the sauce thickens and coats the beef and broccoli evenly.
Serve immediately while the beef is tender and the broccoli remains vibrant.