Coarsely grind sweet corn with green chili and a splash of water.
In a bowl, mix semolina, ground corn, yogurt, salt, sugar, and water; rest for 15 minutes.
Grease a steamer plate with oil.
Stir fruit salt into the batter, pour into the plate, and steam on high heat for 15 minutes.
Heat oil, crackle mustard seeds and curry leaves, pour over the steamed cake, slice, and serve.