Preheat oven to 350 degrees F. Cook macaroni according to package directions; drain.
Meanwhile, in a large skillet cook mushrooms, chopped fennel, and sweet pepper in hot oil over medium heat about 4 minutes or until vegetables are tender, stirring occasionally. Remove from skillet. Add sausage to skillet; cook until browned, using a wooden spoon to break up meat as it cooks. Drain off fat.
In a large bowl combine eggs, ricotta cheese, Parmesan cheese, and pine nuts. Stir in cooked vegetables and sausage. Spoon mixture into cooked macaroni shells.
Spoon about 1 1/2 cups Fresh Tomato Sauce in the bottom of an ungreased 3-quart rectangular baking dish, spreading evenly. Arrange shells on top of sauce. Drizzle shells with remaining sauce and sprinkle with mozzarella cheese. Bake, covered, about 30 minutes or until heated through. Garnish with fennel leaves.
Fresh Tomato Sauce
In a large skillet cook 1 cup chopped onion (1 large) and 3 cloves garlic, minced, in 1 tablespoon hot olive oil over medium heat until onion is tender, stirring occasionally. Stir in 6 cups coarsely chopped, seeded tomatoes; 1 teaspoon salt, 1/2 teaspoon ground black pepper, and 1/4 teaspoon crushed red pepper. Cook and stir about 8 minutes or until sauce is desired consistency. Makes 1 3/4 cups.