The layered look is in!
Spray a 12-cup fluted tube pan with nonstick spray.
Cook carrots in boiling water until tender, 15 to 20 minutes. Drain well.
Microwave or steam spinach for 3 to 4 minutes, until thawed. Let cool, then squeeze dry.
In a food processor fitted with the steel blade, process spinach until finely ground, about 15 seconds. Add contents of one package of gefilte fish and blend well. Spread mixture evenly in tube pan.
Spread with the contents of the second package of gefilte fish to make the second layer.
Process drained carrots about 15 seconds. Add contents of the third package of fish to carrots and blend well. Spread evenly in pan to make the third layer.
Place a piece of Gefen Parchment Paper on top of fish, then cover pan with aluminum foil.
Bake in preheated 350°F oven for one and a half hours. When done, top should be firm to the touch and edges should pull away from sides of pan. A skewer inserted into fish halfway between center and outside edge should come out clean.
Let cool for 20 to 30 minutes. Loosen fish with a long metal spatula. Cover pan with a serving plate, invert and shake gently to unmold. Wipe up any juices that collect on the plate.
Cool completely, then cover and refrigerate overnight.
Slice and serve with bottled or homemade horseradish, lettuce, tomatoes and cucumber slices.