Rinse the clams well and scrub if necessary in cold water. Discard any with cracked or damaged shells and those that don’t close when tapped on the edge of the sink. Set aside.
Preheat the grill to medium.
Combine the crumbs, parsley and lemon zest in a small bowl and sprinkle it over the mullet.
Cook under the grill until cooked through. Set aside.
Fry the pancetta in a medium sauté pan until coloured and remove. Add a dash of oil if needed with the onion, garlic, chilli, rosemary and celery and fry until softened. Add the broad beans and French beans. Sweat gently for 5 minutes.
Meanwhile, cook the pasta in a pan of boiling water according to packet instructions. Drain and set aside.
Heat a dash of oil in a large lidded saucepan, add the clams and vermouth and cover tightly with the lid. Cook for 2-3 minutes, shaking the pan every now and then until the clams open.
Drain the clams and reserve the cooking liquor. Pick through the clams and discard any that have remained shut. Remove the meat from the shells and strain the liquor of any grit.
Add the courgettes and pancetta back to the pan. Add the clam liquor and bring to the boil. Stir in the clams, reserved pasta and the sorrel. Add salt and freshly ground black pepper to taste.
To serve, spoon the clams and sauce into a serving bowl and top with the red mullet.