Heat a little vegetable or peanut oil in a frying pan, add the peanuts and roast over a medium heat, stirring regularly until golden brown. Drain on absorbent paper and cool.
Tightly roll the cabbage leaves together, then slice thinly and place in a large bowl.
Using a mandolin, if possible, thinly slice the carrot lengthwise, then using a sharp knife, thinly slice the carrot lengthwise into julienne.
Add the carrot, onion, tomatoes, prawns and herbs to the cabbage.
Coarsely crush the peanuts in a mortar and pestle and add to the salad.
Combine the vinegar, sugar and chilli flakes in a small saucepan, bring to the boil and stir until the sugar dissolves then remove from the heat and cool to room temperature.
Add enough dressing to generously coat the salad and toss well to combine. Season to taste.
Spoon the salad on to a serving platter and serve as an accompaniment to stir-fried fish and steamed rice.