That's quite a broad swath of I-10 for a chow search!
In Lafayette, try Tsunami for sushi, Pimon for Thai....I'm sure Lafayette has some viet food, but I just haven't found it yet. LC has Pho Tien on Nelson Road & it's worth a visit. New Iberia has Viet Kitchen and Pho Lyly (but I don't know if this second place is still open). If you're driving all the way to BR, the options open up quite a bit. I like Pho Quynh on Florida.....
re: Hungry Celeste
HC is correct...no real Vietnamese here. We do have Mae Son Noodle House, which is a combination of Asian and not too too bad when I need a fix, but no real Viet food. All the Chinese places are buffets (I won't eat off of anything that has to have a sneeze guard) and they are all pretty nasty. Stay on I-10 until you hit Lake Charles if you're looking for Vietnamese.