In a large stockpot over medium heat, add oil. Add onion, carrot, and celery and saute 5 minutes. Add the lentils, bay leaf, turmeric, cumin, coriander, chili powder, salt, and pepper and cook for 30 seconds.
Add the stock, bring to a boil, then lower the heat to low and simmer, covered, for 20 to 30 minutes until the lentils are tender.