Cook onion, carrot, and celery until translucent, add spices, garlic, ginger, and vegetables, then add lentils and chicken. Cover with broth and simmer until tender, about 1 hour.
Shred chicken, return to soup, season, and serve garnished with yogurt, cilantro, and chili flakes.
Notes
For extra flavor, toast the spices well and adjust garnishes to taste.