Prep frozen spinach. Lightly thaw, coarsely chop, drain, and squeeze dry. Combine spinach, mushrooms, and pesto in a medium bowl, stirring to combine; set aside.
Combine the mozzarella, provolone, ricotta, and beaten egg in a medium bowl, stirring well to combine. Then, stir in 1/4 cup Parmesan cheese, and set aside.
Combine the pasta sauce and the tomato sauce in a medium bowl.
Spread 1 cup sauce mixture in the bottom of a six-quart slow cooker coated with cooking spray. Arrange three noodles over pasta sauce mixture; top with 1 cup cheese mixture and one cup spinach mixture.
Repeat the layers, ending with spinach mixture. Arrange three noodles over spinach mixture, and top with remaining one cup cheese mixture and one cup pasta sauce mixture.
Place the last three noodles over sauce mixture and spread remaining sauce mixture over the noodles.
Sprinkle lasagna with the remaining 1/2 cup of Parmesan cheese. Cover with lid and cook on LOW setting for four-and-a-half to five hours (or until desired tenderness is reached). To avoid hardening of noodles, ensure all noodles are covered in sauce or cheese.