Place the chicken thighs, onion, carrots, artichoke hearts, chicken broth, thyme, rosemary, salt, and pepper in the slow cooker. Stir to combine.
Cover and cook on low for 6 hours or until the chicken is very tender.
Remove the chicken to a plate and shred it with two forks. Return the shredded chicken to the slow cooker.
In a small bowl, whisk the flour and milk until smooth. Stir the mixture into the slow cooker to thicken the gravy.
Add the spinach, lemon zest, lemon juice, and parsley. Stir until the spinach wilts and everything is evenly coated in the gravy.
Spoon the mixture over split biscuits and serve.