Add all of your ingredients, EXCEPT for the spinach, cilantro, and lemon juice, to your slow cooker.
Turn the heat on low and cook for 6-8 hours (or until all the ingredients are tender).
Turn off the heat and add your spinach. Stir everything around until the spinach completely wilts in the soup.
Now add the lemon juice, a little at a time, and stop once you reach the taste you desire.
Add the cilantro (if using), and any additional salt and pepper you want, and enjoy!
Serve and enjoy the soup!