In a large skillet over medium-high heat, brown the ground beef until fully cooked. Drain off the excess grease.
Transfer the cooked beef to a slow cooker. Add the diced onion, red bell pepper, crushed tomatoes, and diced tomatoes.
Stir in the minced garlic and Italian seasoning. Pour in the beef broth and gently mix until combined.
Cover and cook on Low for 6 to 8 hours or on High for 3 to 4 hours.
Break the lasagna noodles into bite-size pieces and add them directly to the slow cooker. Stir, cover, and cook on High for 30 to 45 minutes, until the noodles are tender.
Serve hot with a dollop of ricotta, a sprinkle of mozzarella, and shredded Parmesan. Garnish with fresh basil if desired.