The Toffees smashed their transfer record to sign the striker for £28m in July after scoring 16 times in his loan spell from Chelsea last season.
Lukaku did find the net in Saturday's 3-0 win over Aston Villa for what was just his third goal since making the move permanent, but manager Martinez says that there is plenty more to come.
"Goals are always important for strikers," he told reporters. "That's his third goal in the league and that's a good number at this stage.
"But more than anything, I thought it was a really powerful performance from Rom. I've previously said that I don't think he's fully match fit yet and that's going to come.
"But I thought with the intent he had - he looked powerful, he looked very strong - he was a dangerous focal point for us and that's really pleasing."
The Belgium international might fancy his chances of adding to his haul when Everton face Burnley - the only side in the Premier League yet to win a game this season - on Sunday.