Add the turkey and onion to a large skillet and cook over medium heat until the turkey has lost its pink color. Add the garlic and cook for one additional minute. Drain any fat from the cooked turkey. Add 1 1/2 jars pasta sauce and stir to combine.
Combine the cottage cheese, mozzarella, Italian seasoning, and salt.
Add a 1/2 cup meat sauce to the bottom of the slow cooker. Next, add a layer of lasagna noodles and spread 1/4 cheese mixture over noodles. Repeat the layers until these ingredients are gone.
Cover and cook in slow cooker on low-heat until noodles are al dente and cheese is bubbly, approximately 4-6 hours. Remove the lid and add the parmesan to the top. Turn off the slow cooker and allow the casserole to sit for 15 minutes before cutting. If desired, serve garnished with the fresh basil and additional parmesan.