Preheat the oven to 190°C /375°F/gas mark 5 for 20 minutes.
Mix together the breadcrumbs, cheese, onion, herbs and seasoning with 3 tablespoons of milk.
Halve the fillets. Place the largest four halves on the base of a buttered shallow ovenproof dish. Spread the stuffing over the fish and top with the remaining four fillets.
Melt the butter in a saucepan and fry the mushrooms until soft. Add the flour, the remaining milk and the tomato purée and season. Heat, stirring continuously, until the sauce thickens and boils. Pour over the fish. Bake for 20 minutes.
Serve garnished with the parsley and some boiled baby potatoes. Why not try the Carrigaline Farmhouse, Garlic and Herb Cheese for extra flavour.