Cook chicken until fully done if needed. Let it cool completely. Shred it into small pieces using two forks. Small pieces mix better and make each sandwich easier to eat.

Wash the celery, parsley, and onion well. Chop them into very small pieces. Small pieces spread evenly and add crunch without making the sandwich difficult to bite.

Mix mayonnaise, Greek yogurt, Dijon mustard, lemon juice, garlic powder, salt, and black pepper in a bowl. Stir until smooth and creamy with no lumps remaining.

Add shredded chicken, celery, onion, and parsley to the dressing. Stir gently until every piece of chicken is coated. Avoid overmixing to keep the texture light.

Cover the bowl and place it in the refrigerator for at least 30 minutes. Chilling helps the flavors blend together and creates a richer taste.

Use a bread knife to slice each croissant carefully across the middle. Do not cut all the way through. This helps hold the filling inside.

Place lettuce inside each croissant first. Add a generous scoop of chicken salad. Top with tomato slices if you like extra freshness.

Serve immediately while the croissants stay soft and flaky. Pair with chips, salad, or fresh fruit for a complete and satisfying meal.