Combine cooked ground beef, diced tomatoes, taco seasoning, and 1 cup water water in a 5-6 quart slow cooker. Stir, cover, and cook on high 1 hour.
Meanwhile, partially cook pasta shells, cook them in salted boiling water for about 6 minutes. Drain and set aside.
Then add in cream cheese, partially cooked pasta shells, 1 cup shredded cheddar cheese, onion, bell pepper, and ¼ cup water. Stir. Cover and cook another 2 hours on high.
Serve with remaining 1 cup shredded cheddar cheese on top.