Prep the kohlrabi: Trim off the stems and any leaves. Use a knife to peel the tough outer layer, then julienne the bulb into thin matchsticks.
A box grater or food processor with a shred blade also works.
Slice the apples: Core and julienne the apples. If you prefer, leave the skin on for color and extra fiber.
Add the crunch: Julienne the carrot and thinly slice the red onion or scallions. Chop the herbs.
Make the dressing: In a small bowl, whisk together yogurt, mayonnaise (if using), vinegar, Dijon, honey, lemon juice, salt, and pepper until smooth.
Taste and adjust sweetness and acidity.
Toss the slaw: In a large bowl, combine kohlrabi, apples, carrot, onion, and herbs. Pour over the dressing and toss until everything is lightly coated. Sprinkle in sunflower seeds or almonds, if using.
Rest and serve: Let the slaw sit for 10–15 minutes to soften slightly and allow flavors to meld.
Taste again and adjust salt, pepper, or acidity before serving.
Vinaigrette option: If using the vinaigrette, whisk all ingredients in a bowl or shake in a jar, then toss with the slaw as above.