Slice the flank steak against the grain into very thin strips to ensure maximum tenderness.
In a small bowl, whisk together the tamari, honey, minced fresh ginger, minced garlic, and red pepper flakes to create the stir-fry sauce.
Heat the sesame oil in a large skillet or wok over medium-high heat until it is shimmering.
Add the beef strips to the pan in a single layer and sear without moving for 1 minute, then toss and cook for another minute until browned; remove the beef from the pan and set aside.
Add the broccoli florets and sliced red bell pepper to the same skillet along with one tablespoon of water.
Cover the pan with a lid for 2 minutes to allow the vegetables to steam until they are vibrant and crisp-tender.
Return the cooked beef to the skillet and pour the prepared sauce over the mixture.
Toss everything together for 1-2 minutes until the sauce has thickened slightly and coats the beef and vegetables evenly.
Remove from heat and garnish with toasted sesame seeds before serving.