Slice the flank steak against the grain into thin, bite-sized strips.
In a small bowl, whisk together the tamari, grated ginger, minced garlic, and red pepper flakes.
Heat the 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 2 minutes until browned and caramelized.
Remove the beef from the pan and set aside.
Add the broccoli florets and water to the same pan, covering with a lid for 2 minutes to steam until bright green.
Remove the lid, return the beef to the pan, and pour in the tamari sauce mixture.
Toss everything together for 1 minute until the sauce thickens slightly and coats the ingredients.
Turn off the heat and drizzle with toasted sesame oil.
Garnish with sesame seeds before serving.