For the vegetable tempura, place the vegetable oil into a deep, heavy-based 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.)
Place the flour into a large bowl and add enough cold sparkling water to make a thick batter. Season with salt and freshly ground black pepper.
Dredge the vegetables in flour and dust off the excess. Dip the vegetables into the batter, then carefully place into the hot oil. Deep fry for 3-4 minutes, or until golden-brown. Remove from the oil with a slotted spoon and drain on kitchen paper. Place onto a serving plate.
For the dressing, whisk the lemon juice, soy sauce, chilli flakes, salt and freshly ground black pepper together in a bowl. Pour into a small dipping bowl and place alongside the tempura.
To serve, garnish with chives and lemon wedges.