In a liquid measuring cup or small bowl, stir together the peanut butter, soy sauce, rice vinegar, ginger and garlic. Add warm water, a tablespoon at a time, until saucy but still creamy (2 to 4 tablespoons).
In a large bowl, season the cabbage with a pinch of salt. Squeeze until wilted slightly. Add the chicken, cucumbers and dressing. Toss to combine. (Slaw can be made up to this point up to 1 day ahead.) Top with the peanuts and scallions, then crush the nori in your hands and add to the salad.
