Poach the fish gently in about 1 cup of water for between 5 and 10 minutes until the fish starts to flake and is cooked through.
Remove the fish from the pan and drain in a colander to cool.
In a separate bowl place the grated onion , mashed potato, breadcrumbs, finely chopped parsley, egg, garlic paste, finely chopped green chillies, chilli powder, ground coriander , ground cumin ,ground turmeric and salt to taste.
Mix thoroughly to combine.
Flake the fish with a fork and mix gently into the potato mixture taking care not to break up the flakes.
Using your hands, form the fish mixture into 12 patties and place the prepared fish cakes on a tray in the refrigerator for at least 30 minutes to firm up.
Once the fish cakes have chilled, gently toss each one in flour and dust off the excess.
Heat the oil in a frying pan and carefully lower the fish cakes into the hot oil.
Fry gently over medium heat until the fish cakes are lightly golden brown and crispy, then carefully turn the fish cakes over and fry the other side.
Remove from the pan and allow to drain on kitchen paper.
Serve piping hot with lemon wedges, a spicy mayo, or my delicious kumquat pickles and a crisp green salad.