Heat the olive oil in a heavy saucepan over moderate heat for 1 minute. Add the onion, basil, oregano, bay leaf, half of garlic, red pepper, and salt and pepper; cook, uncovered, until the onion is soft-about 5 minutes. Remove 2 tablespoons of the mixture from the skillet and set aside.Reduce the heat to low, add the tomatoes and tomato paste, and cook, uncovered, for 20 minutes, stirring occasionally. Set aside.
Meanwhile, cook the pasta shells according to package directions, omitting the salt. Rinse with cold water and drain.
Preheat the oven to 375 degrees F. To prepare the filling, combine 1/4 cup of the Parmesan cheese in a medium-size bowl with the ricotta cheese, spinach, nutmeg, egg white, the remaining garlic and pepper, and the reserved onion mixture. Mix well.
Spoon half the tomato sauce into an ungreased 9x9x2-inch baking dish. Spoon 3 tablespoons of the cheese filling into each shell, and place in the pan. Repeat until all the shells are used. Top with the remaining sauce. Cover with aluminum foil and bake for 25 minutes. Uncover, sprinkle the remaining Parmesan cheese on top, and bake, uncovered, 5 minutes longer.