The Belgian forward scored three goals in his first five appearances after joining the Toffees from Olympiacos in August.
However, he suffered a hamstring injury in November and has not scored once in six games since the turn of the year.
"I don't think he is firing on all cylinders," said Moyes. "He has not returned in the way I would've liked yet.
"He is still getting used to the Premier League and I think he has to create me more goals and score me more goals. That is what I am waiting for him to do, and he knows that - I have told him that. We are hoping for more.
"I think his form at the start of the season was excellent and we saw what he was capable of. I don't think we have really had that from him since he came back from his injury."
Mirallas has been capped 33 times at senior international level, scoring six goals.