Fry the onions until translucent, crush the potato crisps and stir them and the worcestershire sauce into the onions.
Preheat the oven to 200° C.
Heat the mushroom sauce to almost boiling. Lay the fish fillets in an ovenproof dish and pour on the mushroom soup. Spread the onion mixture on top and cook for about 45 minutes covered in the oven, (uncover for about 15 minutes depending on thickness of the fish).
Check the fish is properly cooked and serve with rice or potatoes and peas.
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