Cook spinach according to package instructions and drain well. Squeeze spinach dry by handfuls and chop fine. In a bowl stir together spinach, ricotta, 1 cup Parmesan, eggs, prosciutto, parsley, and salt and pepper to taste.

Preheat oven to 375 degrees and oil a 13 by 9-inch baking dish.

In a large bowl of cold water soak lasagne squares until softened, about 15 minutes. Drain squares and pat dry between paper towels. Spread 1 cup tomato sauce on bottom of prepared dish. Working with 1 square at a time, spread about 1/3 cup filling along one edge and roll up to enclose filling, leaving ends open.

Arrange cannelloni as formed, seam sides down, in one layer in dish. Spoon 2 cups sauce evenly over cannelloni, covering them, and sprinkle with remaining 1/2 cup Parmesan.

Bake cannelloni in middle of oven 30 minutes and let stand 10 minutes before serving. Serve cannelloni with remaining tomato sauce, heated.