1) Grind the walnuts in a blender, or pound them in a mortar until pulverized. Transfer to a mixing bowl.
2) Add the remaining ingredients and blend well. Place the spread on a flat serving dish and form into the shape of a fish. Decorate by surrounding with parsley (or cress) and unbroken walnut halves.
3) Serve with bread, rolls, crackers, or by itself.
NOTE: The Romans preferred the taste of walnuts with their thin inner skins removed. To do this, drop the walnut meats into boiling water for 30 seconds. Drain immediately, rinse under cold water, and then peel off the thin inner skins.