Peel the carrots and cut into julienne (or use pre-cut matchsticks).
Remove the outer leaves of the cabbage and slice the rest thinly.
Slice the spring onion very thinly.
Combine cabbage, carrots, and spring onion in a large bowl.
In a separate bowl, mix yogurt and mayonnaise, then add mustard, vinegar, sugar, salt, and pepper. Stir in most of the chives (save a little to garnish).
Pour the dressing over the vegetables and mix well.