For the salad: Remove the skin from the chicken and shred the meat with a fork. Toss in a large bowl along with the scallions, red pepper, cabbage, lettuce, bean sprouts, water chestnuts, cilantro, peanuts and chow mein noodles. With a sharp knife, cut the peel from one of the oranges, then cut the segments away from the membranes. Coarsely chop the segments, then add them to the bowl. Slice the other orange in half and squeeze over a small bowl, reserving 2 tablespoons juice.
Make the dressing: Whisk together the reserved orange juice, hoisin sauce, vinegar, ginger and garlic in a small bowl. Slowly add the oil, whisking constantly, until emulsified and thick; season with salt and pepper. Pour the dressing over the salad, then season with salt and pepper. Toss and serve.