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).
Notes
Adding the mozzarella: We recommend adding the shredded mozzarella as a topping for individual servings, rather than stirring it all into the crockpot. As the mozzarella melts, some of its water content will release into the sauce, giving it a thinner consistency. Totally okay if you want a lazy shortcut, but be aware that it will change the texture of the sauce!Serving suggestions: You can serve this crock pot chicken parmesan over pasta, or on sub rolls or slider buns for a delicious sandwich!Storing & reheating: Store leftover chicken parm in the fridge for up to 5 days. To reheat, simply microwave for about 1 minute per serving, stirring halfway through. (Note: Add mozzarella after reheating - the warmth of the reheated food will help it melt!)