1. Preheat oven to 350°.
2. Cook pasta according to package directions, omitting salt and fat; drain.
3. While pasta cooks, heat a large nonstick skillet over medium-high heat. Add oil to pan; swirl to coat. Add zucchini and mushrooms; sauté 6 minutes or until vegetables are tender and beginning to brown. Add garlic; sauté 1 minute. Add spinach and salt; cover, and cook 1 minute or until spinach wilts. Remove pan from heat; cool 10 minutes.
4. Combine basil, next 4 ingredients (through ricotta cheese), and 1/2 cup mozzarella cheese in a large bowl; stir in vegetable mixture.
5. Spread 1 cup marinara sauce over bottom of a 13 x 9-inch glass or ceramic baking dish coated with cooking spray. Stuff cheese mixture evenly into shells. Place shells on top of sauce in dish. Pour remaining sauce over shells. Top with 1 cup mozzarella cheese and Parmesan cheese. Cover with a sheet of foil coated with cooking spray, coated side down.
6. Bake at 350° for 40 minutes or until sauce is bubbly and cheese melts. Let stand 15 minutes before serving.