"Amazing" tableside guacamole and "festive margaritas" followed by Mexican meals that are more "elegant and interesting than expected" set apart this cheery, affordable Inman Square grill; for the same eats without the sit-down experience, some opt for "fast" takeout courtesy of the "friendly" staffers at the "small" Olecito offshoots (one next door, one in Brookline) instead.