Grind the mustard seeds, chiles, salt, turmeric and water into a smooth paste in a blender. Marinate the cleaned shrimps in this paste for at least 10 minutes. Split the coconut in two and drain the coconut milk. The milk is not used.
Put the shrimp mixture in the coconut halves with the mustard oil and the whole chiles. Put the two halves of the coconut together and use a thin rope of dough to seal the joint. Put the coconut in the oven and bake for 45 minutes at 400 degrees. The author suggests that the preferred method is to barbeque the coconut among coals --- The coconut is left in the dying embers until the outer layer is well charred --- about 1/2 hour.
From the Dinner Co-op