In large skillet, cook sausage and onion over medium-high heat until meat is browned and crumbly; drain.
Add cooked sausage and remaining ingredients to 6-quart slow cooker.
Cover and cook on low 2 ½-3 ½ hours until tortellini is cooked.
Stir to make sure sauce is creamy before serving. Top with Parmesan cheese, if desired.
