Heat oil in a large pan and add the mustard seeds, cumin seeds and dried red chilies over medium heat. When the mustard seeds starts popping, add peppercorns, ginger & garlic and fry for a minute. Then add the onion and fry until brown. Add the red chili powder, turmeric and salt and cook for 3 more minutes. Now pour the coconut milk and bring it to a boil over high heat. Then add the crabmeat and mix gently. Simmer and cook uncovered until the crab is cooked. Garnish with cilantro leaves and serve hot with rice.