Cook lasagna noodles to desired doneness as directed on package. Drain.
Meanwhile, heat oven to 350°F. Spray 13x9-inch (3-quart) glass baking dish with nonstick cooking spray. Heat oil in large skillet over medium heat until hot. Add onion; cook 3 to 5 minutes or until tender, stirring occasionally. Add spinach; stir to combine. Remove from heat. Stir in pesto.
In large bowl, combine ricotta cheese, egg, salt, nutmeg and pepper; mix well.
Layer 4 cooked noodles in sprayed baking dish. Spread 1/3 of spinach mixture over noodles. Spread 1/3 of ricotta mixture over spinach mixture. Sprinkle with 1/3 of mozzarella cheese. Repeat layers ending with noodles. Spread Alfredo sauce over top layer of noodles. Sprinkle with Parmesan cheese. Spray foil with cooking spray; cover baking dish.
Bake at 350°F. for 45 to 55 minutes or until thoroughly heated. Cut into squares to serve. Garnish with parsely.