Saute ground sausage and diced onions (could dice up 1 small bell pepper too if desired) in a skillet with a touch of olive oil until meat is no longer pink. Drain and pour into slow cooker.
Pour jar of spaghetti sauce and beef broth on top, stir, cover and cook on low for 4 hours.
Then pour in bag of frozen ravioli, submerge into soup and cover again. Turn heat to high for 1 hour to 1 hour 15 minutes (until tender to your liking).
Spoon into bowls with shredded mozzarella (could add a dollop of ricotta cheese on top too) and enjoy with a piece of bread on the side.