In your 5-6 quart slow cooker, combine the cooked ground beef, diced tomatoes, taco seasoning, and 1 cup of water. Stir well.
Cover and cook on high for 1 hour.
While that cooks, partially cook your pasta shells in salted boiling water for about 6 minutes, then drain and set aside.
After the initial hour of slow cooking, add the cream cheese, partially cooked pasta shells, 1 cup of shredded cheddar cheese, onion, bell pepper, and remaining ¼ cup of water to the crockpot.
Stir everything together, making sure the cream cheese and cheddar cheese start to melt and coat the ingredients.
Cover and continue cooking on high for 2 more hours.
Serve hot, topped with the remaining 1 cup of shredded cheddar cheese.