In a large skillet over medium heat, brown the ground beef or Italian sausage until it is no longer pink. Drain any excess fat.
Add the diced onion and minced garlic to the skillet, cooking until the onion is translucent (about 3-4 minutes).
Transfer the meat and onion mixture to the slow cooker. Pour in the beef broth, crushed tomatoes, tomato paste, oregano, basil, salt, and pepper. Stir to combine.
Add the broken lasagna noodles to the slow cooker, stirring to ensure they are submerged in the liquid.
Cover the slow cooker and cook on low for 4 hours, or until the noodles are tender.
Once cooked, stir in the ricotta cheese and half of the shredded mozzarella cheese. Allow to heat for an additional 5 minutes.
Serve the soup hot in bowls. Top each serving with the remaining mozzarella cheese, grated Parmesan cheese, and fresh basil if desired.