Slice the flank steak against the grain into very thin strips to ensure maximum tenderness.
In a small glass bowl, whisk together the coconut aminos, minced garlic, and grated fresh ginger to create the stir-fry base.
Heat the avocado oil in a large cast-iron skillet or wok over medium-high heat until shimmering.
Add the beef strips in a single layer, seasoning with sea salt and black pepper, and sear for 2 minutes until browned and caramelized.
Remove the beef from the pan and add the broccoli florets and sliced red bell peppers with a splash of water to steam-sauté until crisp-tender.
Return the beef to the skillet, pour in the sauce mixture, and toss everything together for 1 minute until the glaze thickens.
Remove from heat, drizzle with toasted sesame oil, and garnish with sesame seeds before serving.