Preheat oven to 200°C and grease a rectangular dish (38x25cm) with butter. When the the pastry has defrosted lay it in the greased dish, leaving enough to place on top of pie.
In a frying pan fry the mince with a bit of oil and drain most of the fat out, add the tomato paste and the barbecue sauce & cook through.
Lay the meat evenly over the dish.
Put the cheese over the whole thing, put the top pastry on. Place in the oven for 20 minutes or until cooked.