1.Cook rice in large saucepan of boiling water, uncovered, until just tender; drain.
2.Combine chicken, tamarind, garlic, chilli, sugar and juice in medium bowl.
3.Heat half of the oil in wok; stir-fry chicken mixture, in batches, until browned all over and cooked through.
4.Heat remaining oil in wok; stir-fry onion until just softened. Return chicken to wok; toss gently to combine.
5.Serve chicken mixture with rice; sprinkle with coriander, and lime wedges, if desired.
Tamarind concentrate, a thick, purple-black, ready-to-use sweet-sour paste manufactured from the pulp of tamarind tree pods, is available from most supermarkets and Asian food stores.