Coconut Fish Curry with Cauliflower and Potatoes

Name: Coconut Fish Curry with Cauliflower and Potatoes
Ingredients: 11/2 pounds of tilapia fillet, cut into 2 inch sized pieces; 1 teaspoon turmeric; Salt to taste; 2 tablespoons oil (preferably mustard oil); 1 teaspoon nigella seeds or panchphoron; 1 medium sized red onion, cut into a fine dice; 2 teaspoons fresh ginger paste; 1 medium head (about ¾ pound) of cauliflower; 1 medium sized potato, peeled,halved and thinly sliced; 1 to 2 medium sized tomatoes; 2 green chilies finely chopped; ½ cup coconut milk; ¾ cup of water; 2 tablespoons of finely chopped cilantro