To make the chilli jam, preheat the oven to 180 degrees Celsius, pour the olive oil into a roasting tray, add the tomatoes and roast for 20 minutes.
Dry roast the cumin and mustard seeds in a frying pan and, once fragrant, remove and crush with a mortar and pestle.
In a heavy-based pan, combine the spices with the garlic, chilli, ginger, vinegar, rice syrup and fish sauce and heat gently. Add the tomatoes to the saucepan and simmer for 1 1/2 hours, stirring occasionally, until the mixture thickens and looks like jam. Pour into a sterilised jar and seal while hot.
While the chilli jam is simmering, make the fishcakes.
Using a damp, clean cloth, wipe the redfish clean and ensure it is free of scales and skin.
Place the fish, lemon zest, fish sauce, spring onions and seasoning in a food processor and process until the fish is finely minced (ground).
Peel and cut the potatoes into chunks and steam until cooked through. Mash in a bowl with 1 tsp of the olive oil.
Add the fish mixture to the potatoes and fold through the rocket until well combined. With wet hands, mould into eight patties, each about 10cm (4 in) in diameter, and refrigerate until ready to cook.
In a large non-stick frying pan, heat the remaining olive oil and shallow fry the patties for 4 minutes each side, turning once.
Serve the fishcakes with the chilli jam and Italian green salad.