Fornals' secured a 2-0 victory for the Hammers with a stoppage-time goal, which ensured the East London club safe passage into the FA Cup fourth-round.
"The biggest thing I can say about Pablo Fornals is that his work-rate is really honest," Moyes said when speaking after the game.
"I'd like him to show me a bit more Spanish flair at times and the ability to get goals, like he did there, so we're demanding that of him.
"But I have to say his work-rate when he came on against Bournemouth and again tonight was very good."
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