Heat oven to 400°F. Spray 13x9-inch (3-quart) glass baking dish with nonstick cooking spray. Cook manicotti to desired doneness as directed on package. Drain; rinse with cold water to cool. Drain well.
Meanwhile, in large bowl, combine ground beef, spinach, cheese, pesto and egg. If desired, add salt and pepper; mix well. For easier stuffing, place beef mixture in resealable freezer plastic bag; seal bag. Cut about 1-inch hole in bottom corner of bag.
Fill each manicotti by squeezing beef mixture into manicotti; place in sprayed baking dish. Pour pasta sauce over manicotti. Cover with foil.
Bake at 400°F. for 30 to 40 minutes or until filling is no longer pink in center.