The Belgian, who arrived at Goodison Park from Greek side Olympiakos last summer, has seen his first season on Merseyside hindered by a persistent hamstring injury.
But the 25-year-old impressed during the 3-1 win over struggling Reading on Saturday, scoring a 66th-minute goal.
With Croatian forward Nikica Jelavic unable to find goalscoring form in recent weeks, Moyes was glad to see Mirallas looking a potent threat for the Toffees as they chase a UEFA Champions League spot.
The manager said: "Mirallas was a very different player than the one who had been operating in recent weeks.
"He needed to get his fitness back because he was out for a long time. What we saw here was a player who looked like he can score goals and create goals.
"He looks like he's got a goal in him and that gives players a real lift if they think he can finish it off for them.
"That's really important for us because we've needed someone to get on the end of things. Things aren't going Jela's way at present - so to have Kevin providing that threat is really important."