1.Combine tuna, oil, ginger, chilli and lemon grass in large bowl. Cover; refrigerate 3 hours or overnight.
2.Make wasabi cream. Stir wine, sugar and vinegar in small saucepan over low heat; simmer, uncovered, until reduced by half. Cool slightly. Stir in paste and crème fraîche.
3.Drain tuna; reserve marinade. Cook tuna on heated oiled grill plate (or grill or barbecue), brushing with reserved marinade, until browned both sides and just cooked through.
4.Serve tuna with wasabi cream.