Mayor Marty Walsh's Office of New Bostonians has something special planned for its upcoming gala. Singer-actress Vanessa Williams is set to perform and writer Junot Díaz and chef Ming Tsai will both be honored with the We Are Boston Award, which recognizes "individuals who embrace diversity and immigrant heritage." Díaz, who teaches at MIT and won the Pulitzer Prize in 2008 for his novel "The Brief Wondrous Life of Oscar Wao," says Boston's diversity is one of its biggest assets. "Boston is beautiful precisely because of our immigrant communities. Our energy and sacrifice is the dynamo that drives the city forward," said Díaz, who was born in the Dominican Republic, in an e-mail Thursday. "My mother encouraged academic success and hard work. . . . I think she still would prefer that I was a doctor or something practical but, hey, we are what we are." The We Are Boston anniversary gala — this is the 10th year — takes place in November at the Fairmont Copley Plaza.