Heat the oil in a pan with deep sides on medium heat. Fry the onion for about 5 minutes until soft and light golden brown. Push the onion to the side of the pan and add the turmeric, cumin and cayenne pepper. Fry the spices for 1 minute. The frying releases the aromas of the spices and imparts an extra dimension to the flavour of this dish.
Add the lentils to the fried onions and spices