Place CABBAGE, CARROTS, and GREEN ONIONS in a mixing bowl.
In a separate bowl, whisk together MAYONNAISE, (optional yogurt), VINEGAR, DIJON, SUGAR, CELERY SEED, and SALT.
Pour dressing over coleslaw mix and toss to combine.
Serve chilled. Refrigerate in an airtight container up to 5 days. *see recipe footnote
Notes
If you prefer a crispier cabbage slaw, you can serve it immediately. If you like your slaw on the softer side, refrigerate for several hours or overnight before serving.