Slice the flank steak against the grain into very thin strips to ensure maximum tenderness.
In a small bowl, whisk together the tamari, rice vinegar, bone broth, honey, and arrowroot powder to create the stir-fry sauce base.
Cook the soba noodles in boiling water according to package directions, then drain and rinse with cold water to stop the cooking process.
Steam or blanch the broccoli florets for 2 minutes until bright green and slightly tender, then drain and set aside.
Heat the avocado oil in a large wok or heavy skillet over high heat until it is shimmering and near its smoke point.
Add the beef strips in a single layer and sear for 1-2 minutes without moving them to develop a deep, caramelized crust.
Toss the beef, then add the minced garlic, grated ginger, and red pepper flakes, sautéing for 30 seconds until the aromatics are fragrant.
Pour in the prepared sauce and stir constantly as the arrowroot activates and thickens the liquid into a glossy glaze.
Add the cooked soba noodles and steamed broccoli to the wok, tossing everything together vigorously to coat every ingredient thoroughly.
Remove from heat, drizzle with the toasted sesame oil, and garnish with sliced green onions and toasted sesame seeds before serving.