Shred cabbage into thin, uniform strips using a sharp knife or mandoline, aiming for pieces about 1/8 inch thick. Grate carrots using the large holes of a box grater, and slice red onion paper-thin.

Cut apples into thin matchstick pieces, leaving the skin on for extra nutrition and color contrast. Work quickly or toss with a splash of lemon juice to prevent browning.

Whisk together Greek yogurt, apple cider vinegar, honey, and Dijon mustard until completely smooth.

In a large mixing bowl, combine all prepared vegetables and apples. Pour the dressing over the mixture and toss gently but thoroughly using clean hands or large spoons until every piece is lightly coated.

Add fresh parsley, salt, and freshly ground pepper. Taste and adjust seasoning as needed. Cover and refrigerate for at least 30 minutes before serving.