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, bite-sized strips.
Mince the garlic and grate the fresh ginger until fine.
Heat the sesame oil in a large wok or skillet over medium-high heat until shimmering.
Add the beef strips to the pan, seasoning with sea salt and black pepper, and sear for 2-3 minutes until browned.
Remove the beef from the pan and set aside, then add the broccoli florets and sliced red bell pepper to the same pan.
Sauté the vegetables with the ginger and garlic for 4 minutes, adding a splash of water if needed to steam the broccoli.
Return the beef to the pan along with the cooked soba noodles and tamari.
Toss everything together for 1-2 minutes until the sauce is well-distributed and the noodles are heated through.
Plate the stir-fry immediately and garnish with a sprinkle of sesame seeds.