Place the chicken thighs, lentils, onion, carrots, and garlic in the crockpot.
Pour in the chicken broth, then add the thyme, salt, and black pepper.
Stir once to combine the seasonings with the other ingredients.
Cover and cook on low for 7 hours until the lentils are tender and the chicken pulls apart easily.
Remove the chicken thighs, shred them with two forks, and return the meat to the pot.
Stir in the spinach and let it cook for 5 more minutes until wilted.