Add chicken, vegetables, potato, onion, garlic, salt, pepper, thyme, red pepper flakes (if using), water, and Bouillon to your slow cooker. Stir and cover.
Cook for 4-hours on high, or until your chicken can easily be pulled apart with a fork. Shred the chicken right in the pot, or shred on a cutting board and return it to the slow cooker.
Mix your flour and milk together in a small bowl or cup. Pour into the slow cooker and stir. Cook for another 60 or more minutes or until soup is lightly bubbling and slightly thickened.
Stir in parmesan and baby spinach. Serve and enjoy!