Thinly slice the flank steak against the grain into bite-sized strips and season with sea salt and black pepper.
In a small bowl, whisk together the coconut aminos, toasted sesame oil, grated ginger, and minced garlic to create the stir-fry sauce.
Heat the avocado oil in a large skillet or wok over medium-high heat until it begins to shimmer.
Add the beef to the pan in a single layer and sear for 2-3 minutes until deeply browned and caramelized, then remove the beef and set it aside.
Add the broccoli florets and sliced bell peppers to the same pan with a splash of water, covering for 2 minutes to steam-tenderize the vegetables.
Return the beef to the pan, pour the sauce over the mixture, and toss for 1 minute until the sauce thickens slightly and coats every ingredient.
Garnish the stir-fry with sesame seeds and serve immediately while hot.