This plaque is at 288 Old Ford Road, Bethnal Green, just opposite the Pavilion café by West Lake, Victoria Park.
Israel Zangwill (1864–1926) was a Jewish feminist pacifist who devoted his life to the oppressed. He is perhaps most noted for his novel Children of the Ghetto: A Study of a Peculiar People (1892) and his play The Melting Pot (1909), the latter of which popularized that expression, and is famous for the protagonist David Quixano's utopian dream of America:
'America is God's Crucible, the great Melting-Pot where all the races of Europe are melting and re-forming! Here you stand, good folk, think I, when I see them at Ellis Island, here you stand [...] in your fifty groups, with your fifty languages and histories, and your fifty blood hatreds and rivalries. But you won't be long like that, brothers, for these are the fires of God you've come to – these are the fires of God. A fig for your feuds and vendettas! Germans and Frenchmen, Irishmen and Englishmen, Jews and Russians – into the Crucible with you all! God is making the American.'
The full texts of the books are here:
Children of the Ghetto
The Melting Pot