Place rice in one bowl and mung beans in another. Cover each with ¼ c. dried mung beans, hulled water and soak overnight.*
In a large bowl, combine pork, onions, fish sauce, and pepper. Set aside for 30 minutes.
While pork mixture is marinating, drain rice and beans thoroughly. Add salt to rice and stir well.
In a skillet or wok, heat oil over medium heat. Add pork mixture and stir-fry until meat is cooked through but still tender, about 4 to 6 minutes. Remove from heat and set aside.
In a medium saucepan, combine mung beans and about 1 c. water. Simmer over low heat for 20 minutes, or until soft. Remove from heat, drain, and mash beans with a potato masher or fork.
On a countertop, spread out a piece of plastic wrap about 17 inches square. On top of this, place a sheet of aluminum foil of the same size. Place almost half of the sticky rice in the middle of the foil and shape rice into a square layer.
Top rice with a layer of beans, using half of them. Place pork slices on top of beans. Add remaining beans and top off with most of the remaining rice.
Wrap cake by bringing together two edges of foil and plastic wrap. Fold edges over twice and flatten against the side of the packet.
Tuck remaining rice into the two open ends of the packet, covering up beans and meat. Fold the open ends as if you were wrapping a gift. Place packet, folded side down, on another large sheet of plastic wrap and wrap tightly. Tie securely with a long piece of heavy string or twine, lengthwise and crosswise. The packet should be square or rectangular.
Place packet in a large stockpot full of water and bring to a boil. Reduce heat and simmer uncovered for 4 hours, adding water if necessary. Remove from heat and cool for 1 hour.
To serve, slice wrapped packet into 4 slices. Unwrap, arrange on a plate, and serve.