I do admire Neelix’s ability to conjure up delicious dishes out of practically nothing. In this case, an unnamed marsupial! This is obviously a popular dish, as two kilograms of the marsupial wasn’t enough to satisfy demand (VOY: Survival Instinct). In this recipe, the marsupial is kangaroo and the surprise is how delicious it was. Neelix definitely knows what he is doing!
If you’re in the US, kangaroo meat is at least available online - I would be interested to know how widely available it is in shops. Kangaroo is very lean, so like many lean meats, it either needs to be cooked very quickly or for a very long time. In this case a kangaroo stew is slowly cooked before being covered by parsnip mash to create a kangaroo shepherd’s pie variant. If you can’t get kangaroo, you could substitute venison or beef - although that might take away from the ‘marsupial’ part of the surprise!
Replicate your own