Mix the gram flour, yogurt and water. Beat until there are no lumps.
Mash the chopped chile pepper with the side of your knife (or with a mortar & pestal). Set aside.
Put the yogurt mixture into medium saucepan over low heat. Add the garlic-ginger paste, mashed chile pepper, curry leaves, turmeric, cinnamon, sugar and salt. Stir as it heats up. Bring to a boil.
In the meantime, in a very small pan, prepare the tempering. Heat the oil. When the oil is hot, add the mustard and cumin seeds. Let them splutter for a moment. As they start to slow down, add the hing.
Add the tempering to the yogurt mix. Let it boil for another minute or 2, while stirring. Watch out for splatter when adding the tempering.