In a small glass bowl, whisk together Greek yogurt, olive oil, Dijon mustard, and apple cider vinegar. Season with sea salt and pepper. Set aside.

In a large mixing bowl, combine diced chicken, avocado, chopped celery, and red onion. Fold in the chopped hard-boiled eggs gently.

Drizzle the dressing over the mixture and fold everything together until lightly coated. Maintain some chunks of avocado and egg for texture.

Taste and adjust seasoning if necessary. Serve immediately or chill for 30 minutes before serving.