Clean and devein 500 grams of prawns, then marinate them with 1 teaspoon of ginger-garlic paste, 1 teaspoon of red chili powder, 1/2 teaspoon of turmeric powder, 1/2 teaspoon of garam masala, and salt to taste. Set aside for 15-20 minutes.
Heat 3 tablespoons of oil in a pan over medium heat. Add 1/2 teaspoon of mustard seeds and let them splutter.
Add 1 finely chopped onion and 2-3 chopped green chilies to the pan. Sauté until the onions turn golden brown.
Add the marinated prawns to the pan and mix well. Cook for 5-7 minutes, stirring occasionally.
Add 1/2 cup of grated coconut and cook for another 3-4 minutes, until the prawns are cooked through and the coconut is slightly browned.
Garnish with chopped coriander leaves and serve hot with rice or roti.