To make the crepes, in a blender, combine the flour, water, eggs, and salt and blend, scraping down the sides of the bowl, until the batter is smooth. Transfer to a bowl. Heat a 6 to 7-inch skillet over moderately high heat until hot. Brush the skillet with about 1 teaspoon of the olive oil to coat well and heat the oil until hot. Pour 1/4 cup of the batter into the center of the skillet and lift and tilt the pan to coat the bottom with a thin layer. Cook until the batter is set and the underside is golden, about 1 minute more, and invert onto a plate. Make additional crepes with the remaining batter in the same manner. Crepes may be made 1 day ahead. Cover and chill. Freeze for up to 1 month. Defrost in the refrigerator before using.) Preheat the oven to 350 degrees. Lightly oil a large shallow baking dish.
To make the filling, in a bowl combine all of the ingredients, except for the sauce.
To assemble, lay each crepe on a work surface, attractive side down, spoon 3 tablespoons of the filling down the center, and fold in the edges to enclose the filling. Fill the remaining crepes in the same manner. Spoon 1 to 1 1/2 cups of marinara sauce into the flameproof baking dish in an even layer. Arrange the crepes, seam side down, in the dish and spoon on enough of the remaining sauce to coat the crepes. (The dish may be assembled several hours or 1 day ahead. Cover and chill. Allow longer baking time if refrigerated.) Bake for 15 minutes, or until the crepes are heated through and their edges are slightly crisp. Sprinkle with additional Parmesan to taste and put the crepes under the broiler, about 3 to 4 inches from the heat, for 2 minutes, or until the top is golden.
BASIC MARINARA SAUCE
In a deep skillet set over moderate heat, heat the olive oil until hot. Add the garlic and onion and cook, stirring occasionally, until they're pale golden, 5 to 7 minutes. Add the tomatoes, oregano, and salt and pepper to taste, and simmer, stirring occasionally, until the tomatoes have reduced and separated from the oil, 15 to 20 minutes. Add the red pepper to taste, if desired and simmer for 2 minutes more.