Zaza played for Conte at Juventus and with Italy.
He told West Ham’s official website: “It was an honour and a pleasure to play under Mr Conte for Italy.
“He is a coaching genius and a tactical expert and it is interesting to play for him because he is so obsessed with tactics and the movement of players around the pitch.
“He will have to battle against the footballing culture of this country, but I think he will do well here.
“I am happy because this is a big match against a big team on a big stage, and I like playing against big teams! I am also happy because I will be reunited with Mister Conte.”