This word is a shortcut of meaʻono-puaʻa, meaning "pork cake" (meaʻono meaning "cake"). Very similar to the chinese char siu bao sold at many Chinese restaurants.    

http://en.wikipedia.org/wiki/Cha_siu_baau  

Growing up in our plantation camp back in the early 50's,I remember an old Chinese man who would come to our neighborhood and sell Chinese food.  He had an old truck which was retrofitted with glass windows on the sides and the shelves were full of dim sum or Chinese little meals, Hawaiians called the pork buns - "manapuas".  He would park his truck and load a small supply into steamers that hung from each end of a bamboo pole across his shoulders.

He would call out - "Manapua, Manapua!"  Us kids would come running to see what he had.  We wished we could buy his treats, but we couldn't afford to buy them very often.   He went from camp to camp selling his food.  He would park his truck and walk the neighborhoods carrying those heavy baskets. Although his truck was parked and unattended, no one stole from him---amazing!

Fast forward to early 2003 when we opened the restaurant, I was talking to a new customer and she said she was from my hometown of Puhi on Kauai.  We started talking about the old days and the "Manapua Man". That old man was her grandfather.  What a small world!  She also said that he helped send all his kids to college - wow, imagine,  from such meager earnings!  

I was truly humbled by his selflessness and commitment to his family.

   Here's an article that you might be interested in:
http://www.hawaiitraditions.com/2009/08/25/the-manapua-man-then-and-now/  

TOFU LADY:    I was asking my mom  about the Manapua man and she reminded me about the "TOFU lady".   She would take orders for blocks of tofu and would walk from one town to another carrying two heavy metal cracker tins full of her tofu dangling on each end of a stick like the manapua man.  EACH can was probably filled with about 25 pounds of tofu and water.  I figured it was about 3 miles each way.  Can you imagine YOUR mom walking and carrying such a heavy load for miles for 5 cents a block of tofu?   

We cannot fully appreciate the back breaking work that our parents endured.  Plantation life back then meant everyone worked hard.  

 Aloha, Myron