Use strips of aluminum foil to cover down the side, across the bottom, and up the other side of the slow cooker dish. The idea is to have these overlap so you can use them to remove the entire lasagna once cooked. Spray foil with cooking spray.
In a large skillet, cook ground turkey and onion until turkey is browned and crumbly; drain. Add Italian seasoning, garlic powder and salt.
In a small bowl, combine 1 cup mozzarella, ricotta and pesto.
In prepared slow cooker, layer ⅓ marinara sauce, lasagna noodles (break to fit), turkey mixture and cheese mixture. Repeat 2 more times. Cover with remaining 1 cup mozzarella.
Cover and cook on low 3-4 hours or until noodles are tender. Turn off slow cooker and remove crock. Let stand 30 minutes before serving. Use the foil strips to transfer the lasagna to a serving platter, if desired.
Serve with grated Parmesan cheese.