Wash and chop all vegetables uniformly. As I mentioned above, you can peel the vegetables and cut them lengthwise into medium sized pieces. Cucumbers need not be peeled, you can just remove the seeds and cut them up.
In a pan, add the chopped vegetables except tomatoes along with water and salt and bring the water to boil.
Meanwhile grind together the ingredients needed for grinding (without using water) - coconut, green chilies, cumin seeds and curry leaves. You don't have to grind it too much, just grind them for few seconds, so they will get blended together.
As the water starts boiling, add turmeric powder and red chili powder.
Add the cashew nuts also to the pan, if you are using cashew nuts.
Add the mix of coconut blended with spices (the one we prepared by grinding just now).
Close the pan with lid, reduce the heat to low flames and then cook for about 5 to 6 minutes or until the vegetables are cooked enough.
Add chopped tomatoes, cook for another 2 minutes.
Meanwhile beat the yogurt in a bowl to avoid any lumps.
Add the yogurt to the avial, mix well very gently.
Add the coconut oil and curry leaves, mix again gently.
Switch off the stove and transfer the avial to the serving dish.
Avial is ready to be served now, enjoy the avial along with rice and yogurt or sambar or any other gravy for the delicious Kerala style lunch!