In a small bowl, combine the soy sauce, vinegar, lemon juice, sugar, and oil, and whisk until well blended. Bring a pot of salted water to a boil and cook soba noodles until just tender (but not mushy), about 3 to 4 minutes. Drain and rinse under cold water until noodles are cool. Drain well. In a large bowl, combine the noodles, scallions, cucumber, and slaw and toss with soy dressing. Serve at room temperature or chilled, if desired.