Toss the vegetables. Add the coleslaw mix and sliced green onions to a large mixing bowl and toss briefly to combine.
Make the dressing. In a separate bowl, whisk together the mayonnaise, apple cider vinegar, sugar (or honey), Dijon mustard, celery seeds, salt and pepper until smooth and well combined.
Combine. Pour the dressing over the cabbage mixture and toss until evenly coated.
Chill. Cover and refrigerate for at least 30 minutes before serving so the cabbage softens slightly and the flavors meld.
Taste and adjust. Give the slaw a quick toss and taste before serving. Adjust seasoning with additional salt, pepper or vinegar if needed.