Main street burgers have hardly been a treat. But a few years ago young chefs started to launch cool burger joints in hot side streets. In Palma, Badal and Raimundo soon attracted a diverse crowd. The latter contributing largely to the development of Plaça Raimundo (sic) Clar. With his Burger Lab on emblematic boulevard El Borne Adrian Quetglas took the concept a step further.  In the shadow of the tall sycomore trees Burger Lab’s terrace is stage and auditorium at the same time. Some people…