Preheat oven to 400 degrees, line a baking sheet with parchment paper and set aside.
Whisk cream cheese and milk until smooth
Add defrosted frozen vegetables and chopped chicken to the cream cheese mixture and stir until combined
Divide mixture between 6 ramekins.
Roll out chilled puff pastry and cut into 6 circles, 1 inch larger than ramekins. Place one pastry round over each ramekin and pinch to seal. Cut small slits in the top of pastry to allow steam to escape.
Place ramekins on baking sheet and bake for 25 to 30 minutes, or until pastry is golden and puffed.
Remove from oven and allow to cool just slightly before serving.