Spray slow cooker pot with cooking spray; set aside. In a small bowl, mix together mozzarella, ricotta, parmesan, egg, oregano and garlic powder.
Spread 2 tablespoons of pasta sauce in bottom of pot. Sprinkle 1/2 of zucchini over sauce and top with 1/3 of the cheese mixture. Break 2 noodles into pieces to cover cheese. Spread 2 tablespoons of sauce and then layer 1/2 of the spinach and 1/2 of the mushrooms.
Repeat layering, ending with cheese and the remaining sauce. Firmly press ingredients into pot.
Cover and cook over low heat for 4-5 hours. Allow lasagna to rest 20 minutes before cutting into wedges to serve. Spoon a little extra sauce over each serving and top with a basil leaf, if desired.