Add vegan beef to the slow cooker and spread it across the bottom. Pour the water evenly overtop, then sprinkle the diced onions evenly overtop. Cook on high for 1 1/2 – 2 1/2 hours, until the beef is slightly browned and the onions are translucent.
Stir in the garlic. Pour in the marinara sauce, diced tomatoes, and vegetable broth. Stir then let cook on high for another 3 – 3 1/2 hours.
Stir in the pasta and cook on high for an additional 30 minutes. Stir in the mozzarella until melted.
Serve with a dollop of vegan ricotta and a sprinkle of vegan parmesan, if desired.