Thinly slice the flank steak against the grain into bite-sized strips and season with sea salt and black pepper.
Mince the garlic cloves and finely grate the fresh ginger.
Heat the sesame oil in a large skillet or wok over medium-high heat until shimmering.
Add the beef strips to the skillet in a single layer and sear until browned, about 3-4 minutes, then remove the beef and set it aside on a plate.
In the same skillet, add the broccoli florets and a splash of water, then cover with a lid for 2 minutes to steam until they are vibrant green and tender-crisp.
Remove the lid and return the beef to the pan, then stir in the minced garlic, grated ginger, coconut aminos, and red pepper flakes.
Toss everything together for 1-2 minutes until the sauce is well combined and the beef is cooked through.
Transfer to a plate and garnish with sesame seeds before serving.