Place the steak in freezer for a few minutes to firm it up for thin slicing.
Boil a large pot of water to cook soba or pasta; cook at a rolling boil to package directions to al dente.
Very thinly slice meat against the grain with sharp knife.
In large round-bottomed pan, heat 2 tablespoons of the stir-fry oil over high heat. Add meat, season with chili powder and brown 2-3 minutes; remove to plate. Cook in 2 batches if necessary to avoid overcrowding the pan. Add remaining oil and stir-fry the ginger, garlic, scallions, daikon and stir-fry to tender-crisp, 2 minutes. Sprinkle the sugar over the pan and stir in chili paste, Worcestershire, Tamari and stock. Add beef back and season with sesame oil.
Drain soba or spaghetti and add to pan. Toss noodles with beef and sesame seeds, and serve.