Pour water into a wide-bottomed pan and season with salt. Set the pan over a low heat and warm the water to a gentle simmer. Then place the white fish fillets in and cook for 3-5 minutes, though depending on the thickness of the fish it may require a couple more minutes. Carefully remove the fish from the liquid and set aside.
To cook the potatoes pour enough water into a heavy bottomed pot and set over a medium heat. Once the water begins to simmer submerge the potatoes and cook until tender. Drain with a sieve and set aside.
Into a large pan heat 2 tbsp of olive oil over a medium flame. When the olive oil has warmed, add chopped onions and 1 tsp of salt and sauté until the onions have softened. Then add ginger, garlic and serrano pepper chilli and sauté for 60-90 seconds to cook out any rawness.
Next add turmeric powder, chilli powder, coriander powder, garam masala powder, ground fennel seeds, black pepper powder and sea salt and stir for a further 60 seconds to release the aromas of the spices. Remove the pan from the flame.
Add the cooked potatoes to the pan and mash well to incorporate the potatoes into the onion spice mix.
Next flake the poached fish into the mix and fold gently. Taste the mixture for salt and add more if required.
Divide the fish cake mixture into equal portions and make large lime sized balls. Then start by coating the fish cake balls in flour, beaten eggs and finally in the seasoned breadcrumbs.
Transfer the fish cake onto a greased parchment lined baking tray and flatten the fish cake into a hockey puck shape. Repeat the step until all the mixture has been used.
Place in a preheated oven 200°C/180°C fan/Gas Mark 6 for 20-25 minutes or until golden brown. Once cooked remove the fish cakes from the oven and serve.