Heat the oil in a pan and add the mushrooms. Fry for 5 minutes, then add the red pepper and cook for a further 2-3 minutes.
Remove from the heat and transfer to a bowl. Stir in the parsley, breadcrumbs, beaten egg and seasoning and leave to cool.
Preheat the oven to 180C/350F/Gas 4.
Spread a large sheet of foil in the work surface and brush with olive oil. Place one turkey breast in the centre, cut side up and spread with the stuffing, pressing it down in an even layer. Lay the second breast on top, cut side down.
Wrap the foil around the turkey, folding the edges over to make a tight seal. Lift into a shallow roasting tin and cook in the oven for 1 1/4 hours. Leave to cool before unwrapping the turkey.
Roll out about one-third of the pastry to an oblong, lift on to a baking sheet and place the turkey in the centre – the pastry should be large enough to leave a border of about 2.5cm/1in all around.
Roll out the rest of the pastry large enough to cover the turkey, brushing the pastry edges with milk or beaten egg and pressing them together to seal. Decorate the parcel with any pastry trimmings, brushing these with milk or beaten egg to fix in place.
Chill for 30 minutes or until ready to cook.
Preheat the oven to 200C/400F/Gas 6. Brush the pastry with milk or beaten egg to glaze and bake for about 25 minutes or until puffed and golden brown. Serve with a selection of vegetables.
Tip: when cooking the pastry-wrapped turkey, use a baking sheet with a lip or a shallow roasting tin to prevent any juices that run out burning on the bottom of the oven