Heat a large skillet over medium heat and cook the ground beef until browned. Drain any excess fat, then add the diced onion and minced garlic and cook for 2 minutes until the onion softens.
Transfer the beef mixture to the slow cooker. Stir in the beef broth, crushed tomatoes, tomato paste, Italian seasoning, salt, and black pepper.
Cover and cook on low for 6 hours or on high for 3 hours.
Stir in the broken lasagna noodles. Cover and cook on high for 20 to 25 minutes until the noodles are tender.
Turn off the heat and stir in the mozzarella and parmesan until melted. Ladle the soup into bowls and add a generous spoonful of ricotta to each. Use a spoon to swirl the ricotta through the top layer before serving.