We recently returned from a vacation in Kauai. My son is very allergic to peanuts and tree nuts. We were surprised at the small number of actual eating options on the north side of the island, but we ate well in those we visited. We notified all the restaurants of his allergy and all of them were very accommodating. We did not venture too far because of the hurricane. Here is where we ate:
*Hanalei Dolphin (had sushi and fish - ate there 2 nights) - no fried foods due to cross contamination with macadamia nuts in fryer. No dessert because of cc with nuts.
*Smiths Luau (we actually did not eat here due to the hurricane but I had spoken to them at length before our trip and they serve no nuts except coconut (which our son eats) and I think one dessert had macadamia
*CJ's Steakhouse -not our favorite restaurant (kind of like a lower end chain restaurant) but son had a large steak and liked it - all safe except fries
*Kalypso - no fried foods.
*Olympic Cafe - the best out of all of them. manager came out immediately and went over everything.