01 - In a large bowl, toss together the green cabbage, red cabbage, grated carrot, and sliced green onions until evenly mixed.
02 - Whisk together mayonnaise, apple cider vinegar, Dijon mustard, sugar, celery seed, salt, and black pepper in a small bowl until completely smooth and incorporated.
03 - Pour the creamy dressing over the vegetable mixture and toss thoroughly until all ingredients are evenly coated.
04 - Sample the slaw and adjust seasoning with additional salt or pepper if desired.
05 - Cover the bowl and refrigerate for at least 30 minutes to allow flavors to develop and meld together.