Brunoise the white onion and sweat in a little butter until soft and cooked. Add the defrosted birds eye peas to the pan. Cover with boiling veg stock and cook for 2 minutes. Pass out the peas from the stock and blitz until smooth in the thermos. Add a little of the stock if needed. Season and reserve for later. Steam the cockles in a little white wine until open, chill and pick. Pass and reserve the stock for later. Heat 50ml of fish and cockle stock together and emulsify with butter. Heat the potatoes, peas, beans and cockles together. Cook the turbot until just cooked and remove from the pan. To plate, add pea puree to the plate followed by the peas and potatoes, top with the turbot and fennel. Finish with the lemon butter sauce and chicken jus.