Slice and roughly dice the aubergine and courgette, place in a collander and sprinkle with salt making sure all pieces are covered with the salt. Leave for about 30 minutes to drain; this step helps to draw excess water from the aubergine and courgette before they are cooked. Wash off the salt and pat dry.
Preheat the oven to 200 C / 180 C fan / Gas 6.
Add the aubergines and courgettes to a bowl with the onions, garlic and peppers. Toss in olive oil and put in a roasting tin. Cook in the oven until soft, about 30 to 35 minutes. Set aside.
Prepare the crumble while the vegetables are roasting. Put all the crumble ingredients, less the nuts and seeds, into a food processor and mix until you have the texture of bread crumbs. Now mix-in by hand the pine nuts and sunflower seeds.
Assemble the dish: Put in an ovenproof dish the mushrooms and roasted vegetables, then pour over them the passata. Season with salt and pepper. Cover with the the crumble mixture.
Bake at 200 C / 180 C fan / Gas 6 until browned and bubbly, about 40 minutes. Sprinkle with basil leaves and serve.