Scrape coconut flesh properly and make a smooth paste using the coconut-water. Cut coconut-bottom and make it flat so that it can stand inside an oven or a pressure cooker. Cut its head in a slightly bigger round shape, it will help while stuffing. Keep the lid.
For the shrimp
Heat oil in a pan. Add panch phoron masala and let it crackle.
Now add onion and garlic, fry.
Add cooked spices and oil in a large mixing bowl.
Now add the mustard paste, chilli paste, turmeric, salt, coconut paste and coconut water and mix well.
Then add shrimps to this paste and mix well.
Stuff the shrimp mixture inside coconut and seal its lid with dough.
Preheat the oven to 220 degree and cook for about 45minutes.
Alternatively, you can put the coconut inside pressure cooker, add some water to the pressure cooker, and cook over medium heat for three whistles. Let the vapour get released completely. Serve.