In a large saucepan, heat the oil on medium heat. Cook the onions, carrots and celery until the onions are transparent.
Mix in the cornstarch and stir for a few minutes.
Add in the vegetable broth. Bring the soup to a boil, then add the chickpeas, lentils, tomato sauce, salt, turmeric, cumin and black pepper. Reduce the heat to medium then continue to cook for 25 minutes.