In a pan, bring 2 cups water to a boil with turmeric and salt. Add diced ash gourd pieces to this and boil for 8-10 minutes until they are tender. Do not overcook this, the gourd pieces must retain their shape.
Meanwhile, in a mixer jar, grind the chilli, coconut, cumin, rice flour to a fine paste using 3-4 tbsp water. Remove this into a bowl and whisk in the yogurt to get a smooth mixture.
Add this mixture to the cooked ash gourd and bring to a simmer over a low flame.
Do not bring this to a vigorous boil.
Heat the oil in a small pan. Add mustard seeds. Once it splutters, add the curry leaves, fenugreek seeds and red chillies. Once the fenugreek turns golden brown, transfer this tempering over the pulissery.