Prepare the beef by slicing the flank steak against the grain into very thin, bite-sized strips.
Season the beef strips evenly with sea salt and black pepper.
Steam the broccoli florets for 2 minutes until they are bright green and slightly tender, then set aside.
In a large wok or cast-iron skillet, heat the avocado oil over medium-high heat until shimmering.
Add the beef strips in a single layer and sear for 2-3 minutes until browned and caramelized, then remove from the pan.
Reduce heat to medium and add the minced garlic, grated ginger, and red pepper flakes, sautéing for 30 seconds until fragrant.
Return the beef and broccoli to the pan, drizzling with tamari and toasted sesame oil.
Toss everything together for 1 minute to coat and heat through.
Serve immediately, garnished with sesame seeds for a clean and satisfying meal.