This is called Pork Musubi (ポークむすび, the rice ball with Spam and omelette). It is one of a popular Okinawan food. "Onigiri, おにぎり" or "Omusubi, おむすび", is a Japanese food made from white rice formed into triangular or oval shapes and often wrapped in nori (seaweed). But Okinawa style is an unique that is using with Spam and egg.
Okinawa Prefecture (沖縄県: Okinawa-ken) is a prefecture located in southern Japan. It consists of hundreds of the Ryukyu Islands in a chain over 1,000 kilo meters long, which extends southwest from Kyūshū to Taiwan. Long time ago, Okinawa was an independent nation, and was not part of Japan. Thus they have their own cultures that are a bit different from Japanese cultures.
http://en.wikipedia.org/wiki/History_of_the_Ryukyu_Islands
In Okinawa, Spam (can of luncheon meat) is called "Pork". That was brought by the American presence after WW2. Okinawan people practically arrange this economy can-meat by their style. Traditional Japanese riceball is sometimes hard for non-Japanese people to eat. But this Okinawa riceball is good for meat lovers. Moreover Spam is not expensive. This Japanese food helps your economy too.
Ingredients:
Spam (rightly baked)
Egg (for omelette)
Nori (cut in half)
Steamed Japanese rice
See following photos for making
Basically you don't need to add seasonings like salt or soy sauce. But you can use ketchup or mayonnaise for dipping if you want.
