In a large bowl, combine the ground beef, 1/2 cup of the mozzarella, breadcrumbs, egg, oregano, basil, half the onion, and half the garlic. Add a pinch of salt and pepper. Mix until just combined, then shape into a loaf that will fit in your slow cooker.
Place the meatloaf in the center of the slow cooker. Scatter the remaining onion and garlic around it.
Add the cannellini beans, diced tomatoes, and chicken broth to the slow cooker. Season the bean mixture with salt and pepper and stir gently to combine.
Cover and cook on low for 6 hours, until the meatloaf reaches an internal temperature of 160 degrees.
Sprinkle the remaining 1/2 cup mozzarella over the meatloaf. Cover again and cook for 10 more minutes until the cheese melts.
Slice the meatloaf and serve it with the white bean ragù. Top each portion with chopped parsley.