We liked Pizza Corner and Monkeypod, both across the street from Aulani, but they are tourist prices and not what I would consider experiencing local cuisine. Good for a meal, but definitely use your rental car to explore other areas, even outside of both Ko Olina and Kapolei.
I highly recommend a visit to the North Shore - Matsumoto is the main stop for shave ice and we loved it. Kono's is a little quick service place but has amazing food. Haleiwa Beach House is a nicer sit down place in the same area.