Place the lamb pieces, lentils, onion, carrots, and garlic in the slow cooker.
Add the diced tomatoes with their juices and pour in the chicken broth.
Stir in the cumin, coriander, cinnamon, salt, and black pepper until everything is evenly combined.
Cover and cook on low for 8 hours or on high for 4 hours, until the lamb is tender and the lentils are soft.
Taste and adjust salt if needed, then sprinkle with fresh parsley before serving.