Start by browning the ground beef in a large skillet over medium-high heat, then drain any excess grease. Transfer the browned beef to a 6-quart slow cooker. Add the diced onion and red bell pepper, followed by the crushed tomatoes and diced tomatoes. Stir in the seasonings, then pour in the beef broth. Cover and cook on low for 6 to 8 hours or on high for 3 to 4 hours. Remove the lid and break the lasagna noodles into bite-sized pieces, stirring them into the soup—breaking them directly over the slow cooker helps the pieces fall in evenly. Cover again and cook on high for 30 to 45 minutes, or until the noodles are fully cooked. Serve the soup in bowls, topping each with a tablespoon of ricotta cheese, a handful of shredded mozzarella, and a sprinkle of Parmesan cheese.