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.
Slice the mushrooms and sauté in a pan. 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.