In a large skillet over medium-high heat, cook turkey, onion, Italian seasoning, and salt until turkey is no longer pink. Drain.
In a medium bowl, combine ricotta, pesto, and 1 cup of mozzarella cheese.
Spray a 6-quart slow cooker with cooking spray. Spread about 1/3 of the marinara sauce onto bottom of the slow cooker. Place a layer of 3 lasagna noodles on top, breaking noodles as necessary to fit in cooker.
Spread about 1/3 of ricotta cheese mixture on top of noodles. Then add 1/2 of turkey mixture on top. Drizzle with another 1/3 of the marinara sauce and then another layer of 3 noodles.
Repeat with additional layer of 1/3 of the ricotta cheese mixture and 1/2 of the turkey. Top with remaining noodles, remaining ricotta cheese mixture, and remaining marinara. Sprinkle with remaining 1 cup mozzarella cheese.
Cover and cook on LOW for 3-4 hours or on HIGH for about 2 hours. You know it's done when the noodles are tender and the cheese is melted!
Remove lid and allow lasagna to cool slightly (for about 10-15 minutes) before slicing and serving. This will allow it to set so that it stays together nicely in squares!