Preheat the oven to gas 6, 200°C, fan 180°C. Spread out the squash in a large roasting tin with the onions and garlic, drizzle over the oil, season and scatter with the thyme. Toss to combine. Roast for 25-30 mins until tender, tossing halfway through. Set aside to cool completely.

Meanwhile, roll out 500g pastry on a lightly floured surface to a 38cm circle. Lightly grease the base and sides of a 23cm round springform cake tin. Lift the pastry into the tin and gently press into the base and sides to evenly line, leaving a 1cm overhang. Prick the base all over with a fork. Chill for at least 30 mins, or up to 6 hrs ahead.

Put the spinach in a large saucepan, cover with boiling water and leave to wilt. Drain and rinse under cold water until cool; squeeze out as much water as possible. Put the spinach, ricotta, hard cheese, pesto and lemon zest in a bowl, season and mix well.

Preheat the oven to gas 5, 190°C, fan 170°C. Remove the chilled pastry case from the fridge and scatter half the breadcrumbs over the base. Arrange the roasted squash and onions on top in a single, even layer. Top with the spinach mixture. Layer on the roasted peppers, overlapping to create an even layer. Scatter with the remaining breadcrumbs.

Roll out the remaining pastry on a lightly floured work surface to a 24cm circle, then lay it on top of the pie and press the edges together to seal. Trim away any excess, then crimp all the way around. Brush the top of the pie with beaten egg. Make 3 incisions in the centre to allow steam to escape. Place the tin on a baking tray and bake for 1 hr or until the pastry is cooked and golden.

Leave to cool for at least 30 mins before releasing from the tin. Transfer to a wire rack for 2 hrs if serving warm, or leave to cool completely. Once cool, keep in an airtight container in the fridge; it will be easier to slice once it has been chilled. Will keep, covered, for up to 2 days in the fridge.