To make the dressing, place the sugar, lime juice, fish sauce, ginger, garlic and chilli in a small bowl and stir until the sugar is dissolved. Set aside.
Heat a char-grill pan over medium heat. Brush the chicken with the oil and cook for 2-3 minutes each side or until cooked though. Place the chicken, basil, mint, coriander, tomato and onion in bowls and spoon over the dressing to serve. Serves 4.