Chill a food processor bowl and blade in the fridge (this helps to keep the fish cool while it's being mixed).
Heat the oil in a frying pan and cook the onion and garlic with a little salt until soft. Set aside to cool.
When cool, put into the chilled food processor with the fish and egg white and blitz to a paste.
Then add the salt, rice flour, spices and lemon zest and mix again.
Stir through the chopped herbs and the pine nuts.
Taking roughly 2 tablespoons of mix at a time, use wet hands to roll the fish into balls. Refrigerate for at least 30 minutes (or overnight).
When ready to cook, heat the oil in a frying pan over medium heat, add the fish koftas and fry all over for 5-6 minutes or until just cooked through (you may need to do this in batches depending on the size of your frying pan).
To serve, spoon the dilled feta and yoghurt sauce onto a platter, add some pieces of soured cucumber and then top with koftas.
If you want to serve this as a nibble, skewer a piece of soured cucumber on a cocktail stick with a kofta and have the sauce in a bowl ready for dipping.
For the dilled feta & yoghurt sauce: Blitz the feta, yoghurt and dill together in a food processor or with a stick blender until smooth. Season with salt and pepper to taste. Refrigerate until required.