Preheat your oven to 400°F (200°C). Spread the pecans on a baking sheet and toast them for about 8-10 minutes until golden and fragrant.

In a large mixing bowl, combine mayonnaise, Greek yogurt, Dijon mustard, stone-ground mustard, lemon juice, fresh dill, kosher salt, and black pepper. Whisk until smooth.

Add the shredded cooked chicken, halved grapes, chopped granny smith apple, chopped red onion, and toasted pecans to the bowl with the dressing. Fold ingredients together until well coated.

Carefully slice each croissant horizontally, creating a pocket without cutting all the way through.

Spoon a generous amount of the chicken salad mixture into each croissant, ensuring even distribution.

Arrange the filled croissants on a platter for presentation. Enjoy immediately or chill for later.