Heat oil in a large pan, add the cardamoms, cloves and curry leaves. As the spices begin to sizzle, add the onions and sauté till softened.
Then add the green chillies, garlic and ginger; sauté till the onions are light brown.
Add all the spice powders and mix well to combine.
Lower heat and add the yoghurt; mix well to combine with the onion masala
Increase heat to high and cook the masala stirring continuously till oil starts to separate.
Add the prawns, season with salt and mix well. Cook covered on low heat till the prawns are done. (This dish has a dry consistency, but if there is excess water, cook uncovered on high heat for the last 1-2 minutes)
Garnish with coriander leaves.