Slice the flank steak into very thin strips against the grain to ensure maximum tenderness.
In a small bowl, whisk together the tamari, honey, freshly grated ginger, and minced garlic to create the stir-fry sauce base.
Heat the olive oil in a large skillet or wok over medium-high heat until it begins to shimmer.
Add the beef strips to the skillet in a single layer and sear for 2 minutes until browned on the outside, then remove the meat and set it aside.
Add the broccoli florets and sliced red bell pepper to the same skillet with a tablespoon of water, covering with a lid for 2 minutes to steam until tender-crisp.
Return the beef to the skillet, pour in the prepared sauce and the toasted sesame oil, and toss everything together for 1 minute until the sauce coats the ingredients.
Season with sea salt, black pepper, and red pepper flakes, then garnish with sesame seeds before serving hot.