Wash the potatoes, peel them and cut them into long similar sized pieces ( the pieces are thicker than you cut them for french fries).
Cut the tomato lengthwise and keep it separate.
Add the potatoes to a pot or saucepan and add little water.
Switch on the stove, put on high flames and wait for the water to boil.
Once the water starts boiling, add salt, turmeric powder and red chili powder, stir well and close the pot.
Cook in low flames for about 5 to 6 minutes or until the potatoes are almost cooked.
Meanwhile, you can grind together the grated coconut, green chilies and cumin seeds (if using cumin seeds) - it is also fine to add the finely grated coconut and sliced green chilies just like that if you are not using cumin seeds.
Open the pan when the potatoes are cooked ( after 5 to 6 minutes), add the coconut mix ( along with cumin seeds if using), stir everything well. Add the tomato pieces too to the pot and mix well.
Close and cook in low flame for 2 more minutes.
Open the pan and add the yogurt, mix well.
Add curry leaves and oil, gently stir all the ingredients until well combined.
Serve the hot potato aviyal for lunch or dinner along with rice and any other curry!