Spread the diced sweet potato, peppers, onion and mushrooms across a baking tray, and drizzle with oil. Mix thoroughly to coat, then bake at 190°C (Gas Mark 5 / 375°F) for around 1 hour, until they're soft and just starting to crisp up (you can also spread the veggies across two trays to speed up cooking time if you prefer!). Add the kale, and return to the oven for a further 5 minutes, until just starting to crisp up on the edges.

Transfer the roasted vegetables to a mixing bowl, and add the crumbled feta cheese and pumpkin seeds. Season generously. Mix to combine, and set aside to cool.

Roll out the puff pastry, and cut it into a large rectangle (mine measured around 10 x 11 inches, but slightly larger would be okay too!). Lay it onto a chopping board. When the filling has cooled, pile it up in the centre of the pastry, leaving a few inches of pastry around the edges.

Fold the two shorter ends of the pastry tightly over the filling, then do the same with the longer ends, making sure they meet in the middle. Use a little dab of milk to help seal the pastry closed.

Lay a sheet of non-stick baking paper on a baking tray, and spray it thoroughly with oil. Place it face-down onto the top of the pastry parcel. Lift the chopping board and, holding the pastry parcel firmly between them, flip it over so that the parcel is now the other way up on the baking tray. Use your hands to reshape the parcel slightly if needed (e.g. rounding the corners).

Cut two holes in the top of the parcel to allow any steam to escape. If you like, you can also decorate it - use a knife to gently score a criss cross pattern on top, being careful not to cut all the way through, and use any pastry scraps to create little leaf shapes (stick them on with more milk).

Lightly brush the entire parcel with milk, and bake at 190°C (Gas Mark 5 / 375°F) for a further 40 minutes, or until the pastry is golden brown and crispy.