1.Cut squid down centre to open out, score inside in diagonal pattern; cut into 5cm squares. Set aside in small bowl.
2.Combine ginger, half the onion and one of the chillies in small heatproof bowl. Heat peanut oil in small saucepan until moderately hot, then carefully pour hot oil over ingredients in bowl. Slowly add sauce, kecap manis and sesame oil, whisking constantly; cool.
3.Pour two-thirds of the soy mixture over squid; cover, refrigerate 3 hours or overnight. Cover and refrigerate remaining soy mixture.
4.Drain marinade from squid. Cook squid, in batches, on heated, oiled barbecue plate (or grill or frying pan) until cooked through.
5.Toss squid with remaining onion and remaining chilli; serve with the remaining soy mixture.
This recipe can be prepared a day ahead. Cook just before serving.Note