To make the dressing, add the fish sauce, sugar, lime juice, vinegar, water, garlic, and sliced chili to a small bowl. Mix until the sugar dissolves. Pour ⅓ of the dressing over the shredded chicken and mix well.
To a large bowl, add the green cabbage, purple cabbage, carrots, red pepper, red onions, coriander, and mint leaves. Add the remaining dressing and toss well to coat. Then add in the chicken and mix well.
Mound the salad on a large plate and garnish with the roasted peanuts and crispy fried onions.