Cut the fish into ½ inch cubes. Rub with lemon juice and salt. Keep for half hour and deep fry to golden color, drain and keep warm.

In a separate wok sauté the onion in 1 tsp oil for 10 minutes. Drain the oil and add yogurt to the onions. Puree in the blender and return to the wok and stir for 3 minutes in medium heat. Add the ginger garlic paste. When this turns brown add the tomatoes and the masala, stirring until thickened. Put the fish, cover, simmer for 2 minutes and garnish.