Melt the chocolate in a heatproof bowl set over a pan of gently simmering water, then leave to cool slightly. Divide the crushed biscuits between 4 glasses.
Whip the cream cheese and cream with a hand-held electric whisk for about 2 minutes until the whisk leaves a trail, then stir in the melted chocolate and wasabi paste, to taste.
Spoon the mixture into the glasses and decorate with grated chocolate. Serve immediately or chill until ready to serve.