Slice the flank steak against the grain into very thin strips and season evenly with sea salt and black pepper.
In a small bowl, whisk together the coconut aminos, minced fresh ginger, minced garlic, and arrowroot powder to create the stir-fry sauce.
Heat the sesame oil in a large skillet or wok over medium-high heat until it begins to shimmer.
Add the beef strips to the hot pan in a single layer and sear without moving for 2 minutes to develop a crust, then flip and cook for another minute until browned.
Remove the beef from the pan and set aside on a plate.
Add the broccoli florets and sliced red bell pepper to the same pan with two tablespoons of water; cover with a lid for 2 minutes to steam the vegetables until they are tender-crisp.
Return the beef and any accumulated juices to the pan and pour the prepared sauce over the mixture.
Toss everything together for 1 to 2 minutes until the sauce thickens and coats the beef and vegetables in a glossy glaze.
Garnish with sesame seeds and serve immediately while hot.