David Leong didn't set out to change the way a city eats. He just wanted to fill his dining room.Credit: David Leong / Getty Images / Kailey WhitmanSpringfield, Missouri, proudly calls itself the birthplace of Route 66. It's a city where the Mother Road first found its name and where travelers once cruised past neon‑lit motels, bustling diners, and roadside curiosities. But Springfield is also home to another American original: Springfield‑style…