Just had a Labor Day lunch at Madrona Tree, a new restaurant in Arlington Center. Menu is primarily burgers and sandwiches, with sides such as french fries, onion rings, and friend green tomatoes available. They also do frappes. They've only been open a few days.
The space is comfortable, although small. The market themselves as using local/organic ingredients as much as possible, and have a list of the farms they buy from up on the wall.
I had a BLT w/ Avocado slices; my wife had a vegetable burger. Both very ample in size and very tasty. The onion rings were sweet and had a good breading.
I'd definitely go back - its a good ad to Arlington Center. That stretch needed a simple sandwich place.