Mix all spices in small bowl. Sprinkle chicken evenly with 1 teaspoon of the seasoning mixture. Reserve remaining seasoning mixture.
Heat oil in large skillet on medium-high heat. Add chicken; cook 5 minutes per side or until browned. Remove from heat.
Meanwhile, mix stock, lentils, tomatoes, onion, garlic and reserved spice mixture in 6-quart slow cooker. Add chicken. Cover.
Cook 4 hours on HIGH or until lentils are tender, chicken is cooked through, and most of the liquid is absorbed.