Preheat a large skillet and add in oil. Add in the fennel seeds, black mustard seeds, cardamom, ginger, onion, garlic, and chili. Saute until really fragrant, about 5 minutes. Then add in the turmeric powder and cumin powder and saute for another minute
Add in the coconut milk and water and bring it to a boil and then lower the heat to let it simmer for about 15 minutes. The sauce will lightly thickened. Add in the crab meat and squeeze in the lemon juice and have a taste. Season with some salt and pepper to your taste. Turn off the heat when you like the taste. Just before serving, stir in the cilantro leaves on top and serve immediately