Thinly slice the flank steak against the grain into bite-sized strips to ensure maximum tenderness.
In a small glass bowl, whisk together the coconut aminos, toasted sesame oil, grated fresh ginger, and minced garlic to create the stir-fry sauce.
Heat the avocado oil in a large stainless steel skillet or wok over medium-high heat until it begins to shimmer.
Add the beef strips to the hot pan in a single layer, seasoning with sea salt and black pepper, and sear until deeply browned, about 2 minutes per side.
Remove the beef from the pan and set aside on a plate; immediately add the broccoli florets and sliced red bell pepper to the same pan with a tablespoon of water.
Cover the pan for 2 minutes to steam the vegetables until they are bright green and tender-crisp.
Return the beef and any accumulated juices to the pan, pour the sesame sauce over the top, and toss everything together for 1 minute until the sauce thickens and coats the ingredients.
Plate the stir-fry and garnish with a sprinkle of sesame seeds before serving.