Place eggs in a saucepan and cover with cold water; bring to a boil, then remove from heat, cover, and let stand for 12 minutes before transferring to an ice bath.

In a medium mixing bowl, combine the Greek yogurt, Dijon mustard, lemon juice, salt, and pepper until smooth.

Add the drained tuna to the bowl, flaking it with a fork into smaller pieces.

Fold in the chopped hard-boiled eggs, diced celery, and minced red onion.

Gently mix until all ingredients are evenly coated with the dressing.

Garnish with fresh parsley and serve chilled.