Heat the oil in a large deep frying pan, add the pepper and mushrooms and fry for 5 minutes. Mix the cornflour with the stock until smooth and pour into the pan with the apple juice. Add the tomato puree and bring to the boil, stirring until thickened and smooth.
Stir the cooked turkey into the pan, season with salt and pepper, cover and .simmer gently for 10 minutes. Allow to cool.
Drain the turkey and vegetables from the pan, reserving the cooking sauce, and spoon into a 1.1 litre/2pt pie dish or individual pie dishes.
Roll out the pastry on a lightly floured surface and use to cover the pie. Cut any pastry trimmings into leaves, dampen and press on top. Chill for 30 minutes.
Preheat the oven to 200C/400F/Gas 6. Brush the pastry with beaten egg to glaze and stand the pie on a baking sheet. Bake for 40-45 minutes or until the pastry is puffed and golden brown (25 minutes for individual pies). Heat the remaining sauce.
Serve the pie hot with vegetables and the cooking sauce.