Cook sausage and onion in a 10-inch skillet over medium heat 6-8 minutes, stirring occasionally, until sausage is no longer pink; drain. Stir in tomato sauce, basil and salt.(If you can not find bulk sausage use links like Johnsonville sausage and remove casings and proceed the same.)
Mix 1 cup of the mozzarella cheese and the ricotta and Parmesan cheeses. Refrigerate remaining mozzarella cheese while lasagna cooks.
Spoon 1/4 of the sausage mixture into a 5 or 6 quart slow cooker; top with 5 noodles, broken into pieces to fit. Spread with 1/2 of the cheese mixture and 1/4 of the sausage mixture. Top with 5 noodles, remaining cheese mixture and 1/4 of the sausage mixture. Top with remaining 5 noodles and remaining sausage mixture.
Cover and cook on low heat setting 4-6 hours or until noodles are tender.
Sprinkle top of lasagna with remaining 1 cup mozzarella cheese. Cover and let stand about 10 minutes or until cheese is melted. Cut into pieces.