In 10-inch skillet, cook sausage and onion over medium heat 8 to 10 minutes, stirring occasionally, until sausage is no longer pink; drain. Stir in tomato sauce, basil and salt.
In medium bowl, mix ricotta cheese, Parmesan cheese and 2 cups of the mozzarella cheese.
Spray 3 1/2- to 5-quart slow cooker with cooking spray. Into cooker, spoon 1/4 of the sausage mixture. Top with 4 noodles, broken into pieces to fit. Top with half of the cheese mixture and 1/4 of the sausage mixture. Top with 4 noodles, remaining cheese mixture and 1/4 of the sausage mixture. Top with remaining 4 noodles and remaining sausage mixture.
Cover; cook on Low heat setting 6 to 8 hours.
About 10 minutes before serving, sprinkle top of lasagna with remaining 1 cup mozzarella cheese. Cover; let stand about 10 minutes or until cheese is melted. Cut lasagna into pieces.