Preheat the oven to 180°C, fan 160°C, gas 4.
Meanwhile, heat the oil in a heavy-based frying pan, add the onion, celery, if using, pepper and garlic, and fry gently for 10 minutes until really soft. Add the tomatoes, tomato purée and simmer gently, uncovered, for 15 minutes, until thickened.
Meanwhile, cook the pasta according to pack instructions and drain. Put the pasta in an ovenproof dish. Sprinkle the tuna over the top. Cover with the tomato sauce and carefully mix together.
Toast the bread and crumble into breadcrumbs. Sprinkle the cheese, herbs and breadcrumbs over the top. Bake for 15 minutes until the top is golden and the pasta is heated through.