Preheat the oven to 170 °C. Cut the fish fillets into smaller pieces (about 100g each) and set aside.
Now make the tartare sauce. In a small bowl, whisk together the mayonnaise, yoghurt, capers and chopped pickle, then stir in the lemon juice. Season to taste with salt and pepper and place in the fridge to chill.
In a big bowl, combine the flour, baking powder and the contents of the sachet of KNORR Naturally Tasty Chilli Con Carne.
Add the egg and beer and mix gently - be careful not to over-mix.
Heat the oil in a deep, medium-sized pot to 175 °C, using a kitchen thermometer to check the temperature.
Dip the pieces of fish into the batter and carefully place them, a few at a time, in the hot oil. Fry for 5-7 minutes, or until crisp and golden. Be sure not to over-crowd the pot, as this will reduce the temperature of the oil.
Remove the fish from the pot using a slotted spoon and drain on a few layers of kitchen paper. Place the fish pieces on a platter, and keep them hot in the oven.
Now dip the onion rings in the batter and fry them, in batches, until crisp, puffy and golden. Drain well on kitchen paper.
Serve the fish and onion rings piping hot with a fresh crunchy green salad, tartare sauce, and lemon wedges.