In a bowl soak, noodles in very hot water to cover 15 minutes and drain well in a colander.
Reserve half of noodles for another use. With scissors cut remaining noodles into 3- to 4-inch lengths and in a small bowl toss with vinegar and salt to taste.
In a shallow baking pan (or a pie plate works well) dip a round of rice paper in hot water until pliable, just about 15 seconds.
Carefully lay rice paper on a tea towel. Arrange a bit of courgette, then carrot, then cabbage in a row at one end of rice paper.
Spread a small handful of rice noodles over and sprinkle with cashews and green onion. Top with basil leaves, mint and coriander. Tightly roll up rice paper, folding in sides when half rolled.
(Don’t worry if the first one is messy – it usually takes at least one to get the feel of rolling the salad rolls). Repeat with remaining rice paper rounds.
Wrap rolls with damp paper towel, store in a resealable bag and chill.
Salad rolls can be made up to a day in advance. To serve, slice each roll in half diagonally and serve with cashew dipping sauce.
Cashew Dipping Sauce
Bring all ingredients up to a simmer in a saucepot over medium heat. Simmer, stirring occasionally, for 5 minutes. Serve sauce warm or at room temperature.