Thaw the puff pastry overnight in the refrigerator. Let it sit at room temperature for 15 to 20 minutes before use.

Preheat oven to 400°F (200°C). Cut puff pastry into 3-inch squares.

Arrange squares on a baking sheet. Brush with melted butter and bake for 12 to 14 minutes until golden.

Grill or sauté cooked chicken seasoned with salt and pepper for about 6 to 8 minutes until cooked through. Let cool and chop.

Mix chopped chicken, celery, grapes, onion, mayonnaise, and seasoning in a bowl.

Slice baked pastry shells in half horizontally. Fill each with 2 to 3 tablespoons of chicken salad and replace the top.

Serve immediately on a platter for best texture and flavor.