Heat oil in a saucepan. Sauté frozen Birds Eye Chopped Onions and chicken until lightly browned and cooked through. Remove and set aside.
Melt butter in the saucepan, add garlic, flour and cook for 1 minute, stirring continuously. Gently stir in Edgell Sliced Mushrooms and cream. Return cooked onion and chicken to pan. Remove from heat and set aside to cool for 15 minutes.
spoon chicken mixture into a 25cm ovenproof dish and place sheet of puff pastry on top. Trim with a sharp knife and press edges together. Make a decorative pattern on top and cut a 2cm slit in the middle of the pastry.
Brush with egg and bake in a preheated oven at 200°C for 35 minutes or until golden brown. Rest for 5 minutes before serving.