If you don't have cooked chicken, poach or roast about 1 lb boneless skinless chicken breasts or thighs: simmer in simmering water or broth for 12–15 minutes until 165°F (74°C) internal temperature, then cool and shred or dice to measure 2 cups.

In a large mixing bowl combine the shredded/diced chicken, diced celery, diced apple, minced red onion, toasted nuts, and chopped parsley. Toss gently to distribute evenly.

In a small bowl whisk together the mayonnaise, Greek yogurt, Dijon mustard, lemon juice, honey, kosher salt, and black pepper until smooth and slightly glossy.

Pour the dressing over the chicken mixture. Use a silicone spatula to fold everything together until all solids are coated. Taste and adjust seasoning: add up to 1/4 tsp more salt or a squeeze more lemon if desired. Cover and chill for at least 20 minutes to let flavors meld (can be chilled up to 24 hours).

Assembly

If you prefer warm croissants: preheat oven to 350°F (175°C). Lightly brush the cut sides of croissants with melted butter and place on a baking sheet, cut side up. Warm 5–7 minutes until lightly toasted and butter is absorbed. Remove and let cool 1 minute.

Split each croissant horizontally. Place 1/2 cup of mixed greens or a few butter lettuce leaves on the bottom half to create a barrier (this helps keep croissant from becoming soggy).

Spoon about 1/2 cup to 2/3 cup of the chilled chicken salad onto the greens of each croissant (adjust portion to preference). Gently press the top croissant half in place.

Serve immediately. If making ahead, assemble no more than 30 minutes before serving to keep croissants flaky; otherwise store chicken salad separately in the refrigerator for up to 3 days and assemble just before eating.