Mince and mash half of garlic to a paste with 1/4 teaspoon salt, then stir together with spices.
Heat oil in a 12-inch heavy nonstick skillet over medium-high heat until it shimmers, then cook onions, ginger,green chili and remaining garlic, stirring occasionally, until lightly browned, about 5 minutes. Stir in spice mixture and cook over medium-low heat, stirring occasionally, 5 minutes.
Push onion mixture to edge of skillet and put fish in center, then pile onion mixture on top of fish with the Tomato ketchup. water and simmer, covered, shaking skillet occasionally, until fish is just cooked through, 8 to 10 minutes. Transfer to a baking dish and bake for 10 minute at 150 degree centigrade