Crush garlic with red chili powder and vinegar to make a smooth paste.
Heat coconut oil in a pan and sauté onion until translucent. Add green chilies, ginger, curry leaves, and the chili-garlic paste with turmeric; sauté briefly.
Add tomato pieces and cook until softened. Add water, salt, and simmer for 5-6 minutes.
Add prawns and cook for 2-3 minutes until they start turning pink.
Stir in coconut milk, bring to a gentle boil, then immediately turn off heat.
Garnish with fresh coriander leaves and a squeeze of lime juice before serving.