Slice the flank steak against the grain into thin strips and season evenly with sea salt and black pepper.
In a small glass bowl, whisk together the tamari, grated fresh ginger, and red pepper flakes to create the stir-fry glaze.
Heat the avocado oil in a large skillet or carbon steel wok over medium-high heat until it begins to shimmer.
Add the beef strips in a single layer and sear undisturbed for 2 minutes to develop a crust, then flip and cook for 1 more minute before removing from the pan.
In the same pan, add the broccoli florets and two tablespoons of water; cover with a lid for 2 minutes to steam-sauté until tender-crisp.
Remove the lid, add the minced garlic to the broccoli, and sauté for 30 seconds until the aroma is released.
Return the seared beef and any accumulated juices to the pan, then pour the tamari-ginger glaze over the mixture.
Toss everything together for 1-2 minutes until the sauce thickens and coats the beef and broccoli beautifully.
Remove from heat, drizzle with toasted sesame oil, and garnish with sesame seeds.
Serve immediately over the warm cooked brown rice for a complete clean-eating meal.