Add your shredded cabbage and shredded carrot to a large bowl. If you have a food processor, don't forget that some of them have a shredding feature. Use that to shred if you can. Makes things quick.
Add sliced green onions, mayonnaise, yellow mustard, and cider vinegar to your bowl and mix with a spoon to combine everything thoroughly.
Taste the slaw at this point to see if it needs anything else. Add salt and ground black pepper to suit your tastes.
Store in a container in the refrigerator for up to a week.