To prepare mushroom filling, heat oil in a large nonstick skillet over medium-high heat. Add mushrooms; cook 5 minutes, stirring occasionally. Add oregano and garlic; sauté 1 minute. Add wine, and cook for 3 minutes or until liquid evaporates. Stir in tomato paste and 1 teaspoon flour. Remove from heat, and cool. Stir in ricotta cheese, 1 tablespoon Parmesan, 1/2 teaspoon salt, and black pepper.
To prepare Parmesan sauce, place 3 tablespoons flour in a small saucepan. Gradually add milk, stirring with a whisk until blended. Stir in 1/4 teaspoon salt and nutmeg. Place over medium heat; cook until thick (about 3 minutes), stirring constantly. Remove from heat; stir in 2 tablespoons Parmesan. Keep warm.
Preheat oven to 425°F.
To prepare cannelloni, spoon 1/4 cup mushroom mixture in center of each crepe; roll up. Place, seam sides down, in each of 4 gratin dishes or in a 13 x 9-inch baking dish coated with cooking spray. Spoon half of tomatoes over crepes, and top with Parmesan sauce and remaining tomatoes. Sprinkle with 1 tablespoon Parmesan. Bake at 425°F for 15 minutes. Turn broiler on (do not remove dish from oven); broil 3 minutes or until cheese is lightly browned. Garnish with parsley, if desired.