Preheat your oven to 400°F (200°C).

Combine cooked chicken, mayonnaise, chopped celery, sliced green onions, Dijon mustard, salt, and pepper in a bowl to make the filling.

Roll out the thawed puff pastry and cut into 3 to 4 inch squares.

Place a spoonful of the chicken salad mixture in the center of each pastry square and fold over to seal.

Arrange puffs on a lined baking sheet and bake for 15 to 20 minutes until golden brown.

Let puffs cool slightly on a wire rack before serving warm.