Melt a little oil and butter in a frying pan and fry the pimento, chopped fairly small, until soft. Add the onion and chopped bacon and fry gently until just done. Transfer to a bowl. In the remaining fat gently toss the flaked almonds until golden brown. Put them into the bowl with the pimento, onion and bacon and add the prawns and a generous sprinkling of oregano, salt and black pepper. Spoon some of this mixture on each plaice fillet, fold each fillet over the stuffing, secure with a toothpick or cocktail stick and arrange in a shallow buttered fireproof dish. Cover dish with foil and cook in a fairly hot oven Gas 6 (400°F/200°C) for 25 minutes. Before serving heat up the cream (with any juices from the cooked fish) with the finely sliced mushrooms stirred into it and add salt and black pepper. Stir in the lemon juice slowly and pour the sauce over the stuffed fillets.