Cook lasagna noodles till tender. Drain and set aside. Melt the butter in a saucepan. Whisk in the flour and cook over medium heat about 2 minutes. Add the milk and cook till sauce thickens, about 10 minutes. Add salt, pepper and nutmeg to taste. Remove casings from sausage and cook, crumble and drain. Squeeze defrosted spinach to remove excess water. Preheat oven to 350. Assemble lasagna as follows: Spoon a small amount of sauce into a 9x13" baking pan. Add 1 layer of noodles. Cover the noodles with all of the spinach. Sprinkle with 1/4 cup of the tomatoes. Cover with a layer of provolone cheese. Next layer: use noodles, sauce, tomatoes, and a final layer of provolone cheese. Cover with a layer of noodles, then a layer of sauce and sprinkle with parmesan cheese. Bake for 30 minutes. Let stand 10 minutes before cutting.