Add crushed tomatoes, water, tomato paste, olive oil, garlic, crushed red pepper flakes, basil, oregano, thyme, and salt to a slow cooker and stir to combine.
Next, add the chicken breast to the slow cooker, making sure it's fully submerged in the sauce. Cover and cook on HIGH for 4 hours, or until the chicken reaches an internal temperature of 165 degrees F.
Remove the chicken from the slow cooker with a slotted spoon or spider strainer and transfer to a cutting board. Shred with two forks, then return to the sauce and stir to combine.
Cover and keep warm until ready to serve. Optionally stir the shredded mozzarella directly into the slow cooker, or top individual servings of chicken parmesan with shredded mozzarella before serving (see notes).