A hangi is a traditional Maori meal, and has been a matter of excitement for centuries. The word relates to the method of cooking (in a hole in the ground), rather than the food cooked. Usually, a hangi will feature pork, beef, chicken, stuffing of some variety, potatoes, kumara, cabbage, various other vegetables, and a steamed pudding.
To 'put down' a hangi, one starts with a very large fire. Volcanic rocks are then placed in the centre of the fire, and heated until white-hot. While the rocks are being heated (which takes hours), a hole is dug in the ground. The hole should be a little larger than 1 cubic metre. The hot stones are then placed in the hole, and metal baskets containing individually wrapped (usually in aluminium foil) meals are placed on the stones. The baskets are covered with wet sheets, which are in turn covered by wet garden-variety sacks. The dirt from the hole is then shovelled back over the hole, and is pressed down to prevent the hot air from escaping. The water heats and is turned to steam, which then pressure-cooks the food.
The hangi usually takes ~7 hours to cook, from start to finish. If possible, Manuka wood should be used. This is due to the density of the wood (causing the rocks to heat faster), and the flavour of the smoke, which gives a delicate flavour to the kai. If two food-baskets are to be stacked (for a hui or other gathering), meats usually go on the bottom, and the vegetables are placed on the top.
Some information on this writeup has come from Suzy's World. The original website can be found at http://www.suzy.co.nz/suzysworld/Factpage.asp?FactSheet=269.