Heat oil (coconut or veg) in a large pot. Sauté onion until soft, then add ginger, garlic, and chilies for 2 min.
Add mustard seeds, turmeric, curry leaves, and curry powder. Toast 1 min.
Add pumpkin and pandan leaf. Cover almost with water, add 1 tsp salt, and simmer, covered, ~15 min.
Meanwhile, toast coconut in a pan until dark (don't burn!). If possible, blend to a powder.
When pumpkin is nearly tender, stir in coconut, coconut milk, and sugar. Cook 5 min more.
If the sauce is thin, mix 2 tbsp water + 1 tsp cornstarch and add gradually, boiling until thickened.
Serve hot with rice or roti.
