Step 1 In a small bowl, combine the olives, sun-dried tomatoes, parsley, lemon juice and olive oil.
Step 2 Using a very sharp, straight knife, cut the fillet lengthwise in half, and then cut each piece in half lengthwise again, so that you have four long pieces. Cut away the tip ends so that the four pieces are fairly rectangular and of equal thickness. Cut each of the four pieces on the bias into slices one-fourth-inch thick, making clean, sure cuts. There should be at least 16 slices, though the size and shape of the fillets may allow for more or less.
Step 3Place four slices on each of four serving plates. Sprinkle the fish with salt and pepper. Spoon the tomato-olive mixture over the fish and garnish with celery leaves. Serve immediately.