Heresy, perhaps. But I found the substitution for the traditional lamb to be quite delicious, with an even softer and more melting texture. There was less of the punchy gaminess so the seasoning was better with slightly less lemon juice and more black pepper. Kangaroo fillets are also much easier to prepare than lamb rump, as they are completely lean, so there is no thick or gristly fat to cut off. Thus this is a speedy version -- at least, if you live in Australia and have access to kangaroo fillets.