1. In a large saute pan over medium heat add the olive oil, onion and sausage. Cook over medium heat until the onions are cooked through and the meat is no longer pink. About 10 minutes. Then pour in the crushed tomatoes and allow them to simmer until the mixture is slightly thickened.

2. Meanwhile, mix together the ricotta, mozzarella and Parmesan in a large bowl and add a few pinches of salt and pepper to taste.

3. When the sausage mixture is slightly thickened place one quarter of it on the bottom of the slow-cooker. Then place about 2 to 3 noodles on the bottom, breaking them as needed to fit the shape of the slow-cooker pot. Top this with one half of the cheese mixture and one quarter of the sausage mixture. Then add more noodles and another layer of cheese and sausage. Finally, top with another layer of noodles and pour the remaining one quarter of the tomato mixture on top of the noodles. Turn the slow-cooker to low heat and cook for 4 to 6 hours, or until the noodles are completely cooked.