Heat oven to 200°C. Use a rolling pin to shape pastry case into a square; place it in a 20-cm tart tin. Fold edges of pastry over and crimp to make a decorative edge. Prick bottom with a fork. Line pastry case with aluminium foil; fill with uncooked rice or dried beans. Bake 15 minutes. Remove foil and rice and bake until golden, 5 to 10 minutes. Leave oven on.
Slice pumpkin crosswise into 6 mm-thick rounds up to the seeded part. Scoop out seeds. Slice remaining pumpkin into rings.
Place pumpkin and onion in a single layer on a baking tray; drizzle with ½ tbsp oil and sprinkle with salt. Place zucchini on a second tray; drizzle with ½ tbsp oil and sprinkle with salt. Roast until zucchini is tender, 10 to 12 minutes. Remove from baking tray. Continue roasting pumpkin and onion just until tender, about 5 minutes. Reduce oven temperature to 120°C.
Assemble tart just before serving. Sprinkle bottom of tart shell with 1 tbsp parmesan. Top with an even layer of zucchini, half the onion, 1 tbsp parmesan and 1 tbsp basil. Add a layer of pumpkin, the remaining onion, 1 tbsp parmesan and 1 tbsp basil. Arrange roasted capsicum on top. Brush with remaining oil; sprinkle with the remaining parmesan. Heat tart in oven for 10 minutes. Sprinkle with remaining basil and serve.