Sprinkle the breadcrumbs over the base of the pastry. Layer in the beetroot slices, peppers, squash, onions, feta, potatoes, peas and herbs (in that order for a nice rainbow effect), seasoning well between each layer. Beat the eggs and pour slowly over the filling until most of it has sunk through the layers, saving a little to glaze the top. Brush some egg over the overhanging pastry then lay the rolled pastry sheet on top. Press the pastry sheets together, then use some kitchen scissors to trim the excess pastry, leaving about 2cm. Roll the edges in to seal, then press them firmly with a fork. Brush with egg, sprinkle with seeds, then use the fork prongs to mark out 12 portions. Bake for 1 hr 20 mins until the pastry is golden and crisp. Leave to cool completely before slicing, or chill for up to two days before serving.