Ava Gallo, dressed in a white skirt and a black top, on Tuesday got a kind of Broadway break in the Theater District. The 18-year-old from Staten Island, who had appeared in her high school production of Mamma Mia, belted out Thank you for the Music at Ellen's Stardust Diner on Broadway. She had been named one of five winners or Junior Stardusters in the restaurant's first such competition, performing on Tuesday in front of the restaurant's audience.