Wash the dal with water few times and soak it for 30 minutes. In a saucepan boil the dal with two cups of water in medium heat. Check the dal—you could add some water if needed. Boil until it is soft but not broken. In another pan heat the oil and temper cumin seeds and red chili for few seconds. Now add diced onion and fry till translucent. Transfer the dal in to this pan and add turmeric and salt. Let it boil for few minutes. It can be a thick or dilute as per your choice.
Enjoy with rice and pokoras!