Preheat the oven to 375 degrees F and lightly grease a 9 by 13-inch baking dish with 1 teaspoon of the olive oil.
Melt the butter in a medium saucepan over medium heat. Whisk in the flour and cook for 2 minutes, stirring frequently. Add the milk and whisk to combine well. Bring to a boil, stirring frequently, and cook for 5 minutes, until very thick and the floury taste is gone. Season with 1/4 teaspoon salt, 1/4 teaspoon white pepper, and the nutmeg. Remove from the heat and press plastic wrap onto the surface of the sauce so that a skin will not form; reserve.
In a large bowl combine the slightly cooled meat mixture, spinach, ricotta, and 1/4 cup of the grated Parmesan cheese. Adjust seasonings with salt and pepper, to taste.
Arrange noodles flat on a clean work surface. Spoon 1/3 cup of the filling down the center of each square and roll to enclose the filling. Place the cannelloni, seam side down, in the prepared baking dish. Repeat with remaining filling and pasta squares. Pour the reserved bechamel sauce over the cannelloni, making sure to cover the pasta completely. Sprinkle with the remaining 1/4 cup of Parmesan. Bake until heated through and golden and the sauce is bubbly, 45 to 50 minutes.
Cool cannelloni for 10 minutes before serving. Garnish with chopped fresh parsley, if desired.