Prepare the filling
In a large bowl, combine egg, ricotta, spinach, mushroom and zucchini. Mix well.
In a medium bowl, combine crushed and diced tomatoes and their juices, corn, garlic, crushed red pepper (if using), and salt. Mix well.
Assemble the lasagna
Generously coat a 6-quart or larger slow cooker with cooking spray.
Spread 1 1/2 cups of the tomato mixture in the slow cooker. Arrange 5 noodles over the sauce, overlapping them slightly and breaking into pieces to cover as much of the sauce as possible. Spread half of the ricotta-vegetable mixture over the noodles and firmly pat down, then spoon on 1 1/2 cups of tomato sauce and sprinkle with 1 cup of mozzarella.
Repeat the layering once more, starting with the noodles.
Top with a third layer of noodles. Evenly spread the remaining tomato sauce over the noodles. Finish off with the remaining 5 noodles over the tomato sauce.
Set aside the remaining 1 cup of mozzarella in the refrigerator.
Put the lid on the slow cooker and cook on 'High' for 2 h or 'Low' for 4 h.
Turn off the slow cooker, sprinkle the reserved mozzarella on the lasagna, cover and let stand for 10 min to melt the cheese. Serve.