Place one sheet of puff pastry on the base and sides of the pie dish and trim the excess. Blind bake for 15-20 mins.
Meanwhile, heat oil in a large frying pan to medium heat. Using a spatula, fry the meat, breaking up any clumps, add the onions and carrots and cook until the mince has browned and the onions are soft.
In a container, combine the gravy powder and water, mix well. Pour the combination into the mince mixture. Bring to the boil, then simmer for 2 1/2 minutes until the gravy has thickened.
Pour the mince mixture into the pie dish and top with the other sheet of puff pastry. Trim the excess and press the edges firmly to seal.
Cut a small cross into the centre of the top of the pie.
Bake for 25 minutes until the pastry has puffed and turned golden.