In a medium pot, add the cooking oil, and let it heat up for about 10-30 secondson medium-high. Gradually, add in the onions and garlic and sauté for about 3minutes, or until the onions become translucent. At that point, add thelentils, vegetable broth, tomato sauce, turmeric, salt and sweet potato andallow to heat up until boiling. Once you see that the stew begins to boil,reduce heat to medium-low, cover, and allow the lentil stew to cook for about 20-25 minutes, or until the lentils have absorbed the broth. During the last 10minutes of the lentils simmering, mix in the kale, and cover again.