In a large mixing bowl, whisk together the Greek yogurt, Dijon mustard, and lemon juice until the consistency is smooth and uniform.

Fold in the diced celery, minced red onion, sea salt, black pepper, and chopped parsley into the yogurt mixture.

Add the cubed chicken breast to the bowl.

Using a spatula, toss the chicken thoroughly until every piece is evenly coated with the yogurt dressing.

Taste and adjust salt or lemon juice as needed for flavor balance.

Cover and refrigerate for at least 30 minutes prior to serving to allow the flavors to integrate.