Top and tail the ivy gourds. Using the flat of a knife, smash them up until they split a little, but leave them whole. Don't smash too hard, as then they will get mashed up. Heat the oil on a medium heat in a shallow pan, and add the cumin seeds. Let them splutter for about 30 seconds, then add the onion. Fry for about 5 minutes, until the onion is soft.