For the prawns, coat the raw prawns with the chilli and garlic sauce in a shallow non-reactive dish. Cover and leave to marinate for up to an hour.
Heat the olive oil in a griddle pan until smoking. Add the prawns and cook until well coloured (about three minutes each side).
Set the prawns aside in a warm place while you make the salad and dressing.
For the herb salad, combine the ginger and garlic with the olive oil in a pan and gently heat. Once warmed through, remove from the heat and leave to infuse.
Mix the balsamic vinegar, infused olive oil and the caster sugar in a small bowl to make a smooth emulsion.
Lightly toss all the herbs together in a separate bowl. Add the dressing, a little at a time, until the herbs are coated.
To serve, arrange a little of the salad on each of four plates and serve with the prawns straightaway.