Leaving the shells on, slit the back of the prawns and devein. Rinse and put in a bowl with coriander, fennel, cumin, chili powder salt and pepper. Mix and leave to marinate for a few minutes.
In mortar and pestle (or blender) pound the garlic and shallots until fine.
Heat a little oil in pan until hot. Add the curry leaves and stir-fry for about 2 minutes. Add the pounded garlic and shallots and stir-fry until fragrant. Put in the prawns, stir and cook until it is done. Taste for seasoning and serve hot.
Instead of measuring the individual spices, you may also use pre-packaged fish curry powder that's available.