Put red lentils, 2 cups water, turmeric powder and salt in a non-stick pan and mix well. Cover and cook till the lentils are done.
Slit green chillies without cutting through and add to the pan.
For tempering, heat coconut oil in another non-stick pan, add mustard seeds and fenugreek seeds and let them splutter. Add curry leaves and onion and sauté for ½ minute.
Pour the tempering over the cooked lentils and mix well. Add coconut milk and mix well. Cook for 2-3 minutes. Add lemon juice and mix well. Cover and cook for a minute.
Transfer into a serving bowl and serve hot.