Blend grated coconut along with garlic, shallots (small onions), cumin seeds and green chillies into a fine paste. Keep it aside.
Take a pan and add sliced ash gourd or cucumber pieces in 3/4 cup of water. Since ash gourd cooking time is fast, make sure the pieces are not overcooked. To ensure this, cook it over a low flame.
Once the ash gourd is cooked well, add the grated coconut paste and curd to the mix. Leave it to simmer in a low flame. Turn off the stove when the curry is just brought to a boil. Make sure the curd doesn't boil more than a minute or two.
For the tempering:
Heat the coconut oil in a pan and add mustard seeds and fenugreek seeds. Just when they start spluttering, add red chillies and curry leaves. Finally, add turmeric powder and salt.
Saute until it turns golden brown. For more spicy touch, add red chilli powder. Now finally add this mix to the prepared pulissery. Stir it well.
It is best served with hot rice.