Here's the link to one of my latest food recommendation posts. Mild spicy for Thai would be Tabasco level spiciness. I'm sure that the highest levels of spiciness would approach ghost chili level of spiciness so adjust accordingly
As for Vietnamese, my favorite place to eat pho on that side of the island is
Cuu Long in the Pearl Kai Shopping Center. It'd be relatively close to Pearl Harbor so it might be good for a stop after visiting the Arizona Memorial for lunch. Parking is sort of bad despite it being in a strip mall and there tends to be a line (moves pretty quickly though) at popular meal times though. It really is a hole in the wall but the food is really good.
The closest one to Aulani is going to be
Highway Inn in Waipahu. Great food, excellent pipi kaula. But portions are kind of small and prices are high (there's a reason why my friends and I also nicknamed it "Highway Robbery"
). Farther away, good places are
Young's Fish Market in Kalihi (one of my favorites) and
Yama's Fish Market in Honolulu (more of a take-out place in town) - used to go here all the time when I used to live nearby. The classic places are
Helena's Hawaiian Foods on North School Street (in town near Pali Highway) and
Ono's Hawaiian Foods in Kaimuki (near Waikiki).
My guess is that Young's will be your best option if you're driving back from town, or visiting some place like the Byodo-In (if you're coming back from the Windward side, taking the Likelike Highway (lee-KAY-lee-KAY) will plop you into Kalihi at the end of it, close to Young's) or if you're coming back on Pali Highway, you'll end up close to Helena's. Most likely will need GPS to find any of these places though.