Soba is made from buckwheat, a gluten-free grain, so it's good for people with celiac disease. Some brands of soba also contain wheat -- check the ingredient list.
In a large pot of boiling water, cook soba according to package instructions. Meanwhile, in a large bowl, combine soy sauce, vinegar, oil, sugar, garlic, and ginger.
Drain soba, rinse with cold water, and drain again. Transfer to bowl with soy mixture and toss. Add chicken, scallions, and cabbage and toss to combine.