On the North Shore of O`ahu, between Haleiwa and Kahuku, are a string of shrimp and prawn trucks that serve scampi and similar type dishes (around $10 a plate).

Over at Honolulu Harbor, there is another hot-spot that the locals like; I hear they procure their fish straight from the auction next door.

http://www.nicospier38.com/

In general, any decent restaurant's "catch of the day" is going to be only a day or two old at the most.

This place sounds like something you'd like:

http://shorebirdwaikiki.com/grill1C.htm