Mix three tablespoons of lemon juice, mayonnaise, yogurt or sour cream and the grated Parmesan cheese to make a lemon-Parmesan sauce. Save the rest of the lemon juice for later use. Drizzle the olive oil over the fillets and sprinkle the rest of the lemon juice on top. Broil the fish for about 5 to 6 minutes. Then, top the fillets with 1-2 tablespoons of the lemon-parmesan sauce, and broil for a further 2 to 3 minutes, until the top becomes golden-brown in colour. Place the fish on a serving dish and garnish with slices of lemon and chopped parsley. Makes 4 servings.