Heat a medium pan to medium/high heat. Cook ground beef until it browns (5 minutes), drain and remove from the pan and pour into slow cooker. Wipe the pan with a paper towel and add 1 tablespoon oil to the same pan, cook the onions for 2-3 minute, until soft. Add the minced garlic and cook for another 20 seconds. Turn off heat and pour onions and garlic into slow cooker. Add the jar of marinara sauce, diced tomatoes, italian seasoning, water, and salt. Cook on medium heat for 4 hours. Next, Add the pasta, heavy cream, half the mozzarella cheese, the parmesan and gently stir. Top with the remaining 1/2 mozzarella cheese and cook for another hour or until the cheese is melted and bubbly. Serve warm. Enjoy!