My kid's preschool class did a field trip to Red Line Burger in Lynnwood, (20801 HWY 99), and afterwards he told me about it. My 5-year old is a Chowhound!
Anyway, they have fantastic burgers. They use hormone free beef, and dang, they taste great, cause they're made to order. There are only four main variations of burgers, and so far, I've tried three. My favorite is the Wheelie, which is Teriyaki basted with grilled pineapple. The owner said they usually shoot for medium rare burgers, but will go more rare if you ask for it.
They also do baskets, (Cod, Prawns, Oysters, Chicken strips). I had the Oysters which were ok, but I think the burgers here are the stars. I have to say though, the fries are on the soggy side. My kids love watching the raw whole potatoes go into the fry maker which cuts them into strips before frying. The fries are sprinkled with sea salt, and taste best at the start, but as they cool, they do start getting limp and sad.
Onion rings are hot and crispy though. I've yet to try the deep fried Mushrooms, but that's next!
It's a clean, tiny place, with about 4 tables, and a counter. I highly recommend the burgers!