Spray the inside of a 3-quart slow cooker with cooking spray.
In a small bowl, mix together the ricotta cheese, 1/2 cup of the mozzarella cheese, Parmesan, parsley and several grinds of black pepper. Set aside.
Spread 1/4 of the marinara sauce in the bottom of the crock. Place 1 1/2 to 2 lasagna noodles on top, breaking into pieces as needed to make them fit. Spread with 1/2 of the ricotta cheese mixture. Top with half of the vegetables, another 1/4 of the sauce and 2 more lasagna noodles. Repeat this layer, ending with the last of the noodles and topping with the remaining 1/4 of the sauce.
Cover and cook on high for 2-3 hours or low for 4-6 hours, until noodles and vegetables are cooked through. Turn off heat. Uncover and sprinkle the remaining 1/2 cup of mozzarella cheese on top; recover and allow to rest for 5-10 minutes, or until the cheese is melted.