Wash and pat dry the fish fillet. Rub in salt and pepper.
Heat olive oil in a fry pan or grill pan and sear both the sides of the fish well, till done.
Crumble the fish and set aside.
Wash the potatoes well and cut into thin roundels.
Heat water with salt till it boils, then leave the potatoes in low flame for around 5 to 7 minutes. Switch off and drain.
Heat olive oil in a sauce pan. Fry the ginger garlic paste till a nice aroma comes.
Add the onion and celery and saute till the onion wilts.
Add the flour and fry for a couple of minutes. Now add in the milk and stir till there are no lumps. Cook on low flame till the mixture thickens.
Add in salt, pepper and dried parsely. Switch off.
Preheat oven to 180 degrees. In a deep baking pan. put the crumbled fish, top it with the potatoes. Pour the sauce all over it and then sprinkle generous cheese on top.
Bake for around 30 minutes or golden brown, with the sauce bubbling. Serve hot...