I was travelling alone and was on a bit of a budget (all my money went to tours and "experiences". Well worth it!) I wanted to eat at smaller local places instead of at the resorts. If a sign looked interesting, I would stop and investigate.
I stayed at the Best Western in Kapaa, a serviceable hotel in a good central location. No restaurant on site, but adjacent to the Coconut Marketplace and a quick walk/drive into Kapaa.
Bubba's Burgers - Kapaa and Hanalei
I went to the Hanalei location, the meat had a wonderful "gamey" flavor, I understand it to be local. It was a decent burger, but not as great as the commercials made it out to be.
Eggberts - Kapaa in the Coconut Marketplace
Great breakfasts here, I had banana/pineapple pancakes with coconut syrup. A good choice for filling up before a big day.
Wahoo's - Kapaa
A nicer seafood/steak place in Kapaa, dinner entress range from $18-$30, not outrageous. I had a wonderful piece of fish, grilled with a spice rub and served over garlic mashed potatoes and spinach. Great plating, relaxed atmosphere. Try to sit on the patio in the back, not facing the road.
Sushi Blues - Hanalei
The head sushi chef, Jeff (or Geoff?) was wonderful to chat with, really believes in what he is doing and very concerned with making you happy. I recommend sitting at the sushi bar for best sushi service. Somewhat limited selection and maybe not the best fish (fresh, just not outstanding in flavor...but I'm spoiled with sushi...) Really fancy rolls as well. Huge cuts of fish.
Dolphin Fish Market - Hanalei
I grabbed a pre-made crab sushi roll here for a snack. Fresh crab, HUGE roll, probably about 10 inches in length. Great to bring to the beach. The fresh fish looked great for a bbq or in room cooking.
Shrimp Station - Waimea
Shrimp served several ways, with sauce, battered and fried, etc.
Casual, outside only tables. I had the garlic shrimp, $11 got me a big plate with rice (or potatoes) and lots of saucy shrimp. Messy to eat (they had to be peeled) but worth it. There is a wash up sink on the right side of the building.
Across from the shrimp station was a bakery/granola factory, got some Cornflake cookies that where amazing. Also had a granola parfait with fresh fruit, very refreshing. I think the place was called Sugar Cane Snax
Hanapepe Cafe - Hanapepe
Excellent Gazpacho (a special the day I was there) Lots of vegetarian options, a really nice setting with a good looking menu.
House of Noodles - Kapaa
I had to sample the local Saimin. Very tasty soup, but a little hard to eat on a humid 80 degree evening. The pork dumplings in the soup were excellent. The chicken was very tasty as well, I'm assuming it was local.
Oki Diner - Lihue
Serviceable, but not great. Open until 3AM or so, one of the few places on the island open that late. Breakfasts looked okay, I had Mahi Mahi in butter/wine/garlic sauce with rice. Enough food for 2.
That's my lower rent foodie tour of Kauai.