Remove the first outer layer of the green and purple cabbage. Cut in half and remove the core. Slice thinly and place in a large bowl. Note: see recipe images for reference.Remove any damaged part of the spring onion and slice thinly. Place in the same bowl as the cabbage. Peel the carrots and grate. Add the carrots the large bowl as well.
Add the mayonnaise, Dijon mustard, vinegar, sugar, pepper and salt. Mix until well combined.
Serve immediately or cover and refrigerate for up to 3 days.