Thaw Puff Pastry Dough in your refrigerator overnight.
Preheat the oven to 400° F.
Allow pastry sheet to come to room temperature.
In a large skillet, melt the butter over medium heat. Cut Chicken into 3/8" cubes and cook until just cooked through and white on all sides. (Do NOT overcook.) Set aside and cover to keep warm.
Add the onion and cook for about 2 minutes, until tender. Whisk in the flour, salt, pepper, and oregano until well blended. Slowly stir in the broth and cream, cooking until bubbly and thickened to your desired consistancy.
Microwave frozen vegetables per package instructions.
Stir in the chicken and mixed vegetables and allow to heat through for just a few minutes. Remove the pan from the heat and set aside while preparing the dough.
Roll the sheet of pastry dough out onto a lightly floured board. Cut out four circles about 1" larger than your ramekin dishes, using an inverted dish as a template. You should get 4 circles from one sheet. Discard the trimmings.
Spray the inside of each dish with nonstick spray. Spoon the chicken mixture into each dish, filling completely with a slight hump in the middle of each dish. Place a Puff Pastry Dough circle on top of each cup, folding the overhang inward and crimping into fluted, double thickness pie-like edge. Cut three leaf-shaped vents in each crust.
Bake for 15 minutes, or until the crusts are golden brown and the insides are bubbling. Allow to rest for 5 minutes before serving.