1. Preheat the oven to 200°C. To roast the vegetables, put all the prepared vegetables into large non-stick low-sided roasting tin, making sure not to overcrowd it, as this will make the vegetable pieces become soft. Drizzle over the olive oil and season with salt and pepper, then toss to coat.
2. Place the roasting tin in the oven for about 30 minutes or until the vegetables are cooked through but haven’t become slightly scorched around the edges. Remove the tray from the oven and allow to cool.
3. To make the potato pastry, sift the flour into a bowl with plenty of seasoning. Rub in the dairy free pure sunflower spread until the mixture resembles fine breadcrumbs. Mix in the mashed potatoes and egg yolk until you have achieved a soft dough. Knead lightly into a ball and then wrap in cling film. Chill for at least 10 minutes to rest (or for up to 24 hours is fine, if time allows).
4. Gently roll out the pastry to a 25cm round on a lightly floured surface. Transfer to a baking sheet lined with non-stick baking paper and pinch the edges to make a rim. Spoon the roasted Mediterranean vegetables over the pastry and sprinkle with the crushed chillies, if using. Bake for 25-30 minutes or until the pastry rim is golden brown. Serve cut into slices with some salad, if liked.