Heat oil in a deep pan and sauté ginger-garlic paste until fragrant. Add in the onions and sauté until golden brown.

Next, add mustard seeds, cumin powder, coriander powder, garam masala, and chilli powder. Let all these spices sauté for another 2 minutes until well combined.

Toss in some chopped tomatoes and green chillies and give it a good mix.

Cover the dish and let the tomatoes simmer on a low flame for about 5 minutes or until they soften and meld into the gravy. 

Once that's done, take off the lid, add some water, and crank up the heat to high, allowing the gravy to thicken and ensuring all the ingredients are nicely combined.

Toss the prawns into the gravy and give it a good stir for about a minute. 

Then, cover the dish and let the prawns cook for around 1 to 2 minutes.

Finish it off with a sprinkle of fresh coriander for that perfect touch.