Grease 19cm deep square cake pan; line base and sides with 2 strips baking paper, extending paper 2cm above sides.
Stir chocolate with a metal spoon in medium heatproof bowl over saucepan of simmering water until melted.
Cool 5 minutes.
Combine remaining ingredients in large bowl. Stir in chocolate, working quickly; spread mixture into prepared pan.
Sprinkle over extra coconut.
Refrigerate for 2 hours or until firm before cutting.
