Heat oil in a non-stick pan, add curry leaves and onions and saute till brown.
Put ginger, garlic, dried chillies in a mixer jar. Quarter tomato and add to the mixer along with coconut, fennel seeds and 3 tbsps water and grind to a smooth paste.
Add ground paste to the pan and cook for 2-3 minutes.
Put the prawns in a bowl, add salt, turmeric powder and red chilli powder and mix well. Set aside to marinate for about 5 minutes.
Slit green chillies without cutting through and add to the pan and mix well. Add marinated prawns and mix well. Cover and cook till the prawns are done. Add garam masala powder and mix well.
Transfer into a serving bowl and serve immediately.