Thinly slice the red cabbage using a sharp knife or mandoline.
Julienne the apple into thin matchstick slices (leave the skin on for extra fiber).
Shred the carrot using a grater or food processor.
Mix the slaw:
Add the cabbage, apple, and carrot to a large mixing bowl. Toss gently to combine.
Make the dressing:
In a small bowl, whisk together the lemon juice (or apple cider vinegar), olive oil, honey or maple syrup, Dijon mustard (if using), salt, and pepper.
Combine:
Pour the dressing over the slaw mixture. Use tongs or clean hands to toss until everything is well coated.
Let it rest:
Allow the slaw to sit for 10–15 minutes at room temperature (or refrigerate) so the flavors can meld.
Serve and enjoy:
Sprinkle with chopped parsley and optional seeds before serving.