Combine the cumin, coriander, mustard, peppercorns, turmeric, and red pepper in the jar of an electric blender and blend at high speed until the spices are completely pulverized. (You may also crush them using a mortar and pestle, or as I do, in a coffee grinder I use exclusively for grinding spices) Heat the oil in a heavy skillet over moderate heat and add the onions, garlic, and ginger. Cook for about 5 minutes, stirring frequently, until the onions are soft and transparent but not brown. Add the pulverized spices and continue cooking and stirring for 2 to 3 minutes, then add the tomatoes, water, and salt and bring to a boil over high heat. Cook briskly for 2 to 3 minutes, stirring constantly, until most of the liquid has evaporated. Add the shrimp and stir to combine them with the vegetable and spice mixture. Reduce the heat to the lowest setting and cover the pan, simmering for about 5 minutes until the shrimp are firm and pink. DO NOT OVERCOOK. Remove the pan from the heat and add the lime juice. This dish is traditionally served with mango chutney and boiled rice.

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