Prepare the Vegetables: Shred the cabbage and carrots using a box grater or a food processor. Chop the green onions into thin slices. Combine the vegetables in a large mixing bowl and toss them together.
Make the Dressing: In a separate medium bowl, whisk together the mayonnaise, apple cider vinegar, sugar, Dijon mustard, salt, and black pepper. Mix until smooth and well-combined.
Combine Vegetables and Dressing: Pour the dressing over the shredded vegetables. Toss until the veggies are evenly coated with the creamy dressing.
Chill and Serve: Cover the bowl and refrigerate the coleslaw for at least 1 hour to let the flavors meld together. Stir before serving to ensure an even distribution of the dressing.