Take the cleaned prawns in a bowl. Add the onion paste, coconut paste, green chili, coriander powder, turmeric powder, red chili powder, garam masala powder, salt, coriander leaves, green part of the spring onion and ginger garlic paste.
Mix everything well and refrigerate for 30 minutes.
Heat oil in a pan and add the onion and white part of the spring onion. Fry till brown.
Add the marinated prawns and cook on high heat till it boils.
Once it starts boiling, reduce the heat and cook till the prawns are done, and all the water has dried up.
Remove from heat when oil starts separating.