Place the chicken breasts in the bottom of the slow cooker.
Add the lentils, onion, carrots, celery, garlic, and diced tomatoes on top.
Pour in the chicken broth and add the spices (cumin, smoked paprika, turmeric, salt, and pepper).
Cover and cook on low for 6-8 hours or on high for 3-4 hours, until the chicken is fully cooked and the lentils are tender.
Remove the chicken, shred it with two forks, and return it to the slow cooker.
Stir everything together and taste for seasoning, adjusting if necessary.
Serve hot, garnished with fresh parsley if desired.