Marinate the prawns with turmeric powder and a little salt. Keep aside.
Heat oil in a pan, when smoking hot, flash fry the prawns, a minute or so, till they just change colour, keep aside.
To the same oil, add the cumin seeds, red chillies and green chillies. Saute for a minute or so.
Throw in the garlic, fry for just a minute. Add the sliced onions, cook till they are golden brown.
Now add the tomatoes, sprinkle salt and pepper. Cook for 4-5 minutes.
Throw in the capsicum strips, stir-fry for another 3-4 minutes.
Add the fried prawns, mix well.
Cover and cook for another 5 odd minutes. Adjust seasonings.
Serve hot.