Cook the soba noodles in boiling water according to package directions, then drain and set aside.
Slice the flank steak against the grain into very thin strips and season with the sea salt and black pepper.
In a small bowl, whisk together the tamari, minced garlic, and grated fresh ginger to create the stir-fry sauce.
Heat the toasted sesame oil in a large skillet or wok over medium-high heat until shimmering.
Add the beef strips to the pan in a single layer and sear for 2 minutes until browned, then remove and set aside.
Add the broccoli florets and sliced red bell peppers to the same pan, stir-frying for 3-4 minutes until tender-crisp.
Return the beef to the pan along with the cooked soba noodles and pour the tamari sauce over everything.
Toss well for 1 minute until the sauce thickens slightly and coats every ingredient beautifully.
Serve immediately garnished with a sprinkle of sesame seeds for a delicate crunch.