For the salad, place all the salad ingredients into a bowl and mix well. Place the salad onto a serving plate.
For the onion rings, place the vegetable oil into a deep, heavy-bottomed saucepan and heat until a small cube of bread sizzles and turns golden when dropped into it. (CAUTION: hot oil can be dangerous. Do not leave unattended.)
Dredge the onion rings in the seasoned plain flour.
Place the self-raising flour into a large bowl, add the sparkling water and salt and whisk to make a thick batter. Add more sparkling water if necessary.
Dip the floured onion rings into the batter, then carefully place into the hot oil. Deep-fry for 3-4 minutes, or until golden and crisp.
Remove the onion rings with a slotted spoon, drain on kitchen paper and sprinkle with salt.
To serve, top the salad with the onion rings.