in a medium skillet over medium high heat, cook Italian sausage and onion until completely browned.
Stir in pasta sauce and salt.
Lightly grease a 2.5-4 quart slow cooker (not the deep round kind, but an oval one with more surface area).
Spread a little bit of sauce on the bottom of the slow cooker to prevent sticking.
Place 3 lasagna noodles in the bottom of the slow cooker, breaking to fit (save any broken pieces to fill in gaps later). Spread with ⅓ sauce, and top with ⅓ mozzarella and ⅓ Parmesan.
Repeat layers two more times.
Put the lid on and cook on low for 2.5-3 hours, until noodles are softened.
Turn the slow cooker off and allow to sit for 10 minutes before slicing and serving.
