Lukaku scored twice in the first half of a 3-2 win for the Toffees while making his first home appearance for the club.
Martinez was particularly happy with the 20-year-old's awareness and believes that he will only get better as the season goes on.
"For a number nine to have that awareness of what was going on around him, Romelu Lukaku was unplayable," Martinez told BBC Sport.
"He is going to get stronger and the players around him will learn how to play with him."
Martinez also reserved special praise for Ross Barkley, who scored his side's other goal in a dominant first-half display for Everton.
"Ross Barkley is the sort of player who controls things in midfield that is unusual in a player his age. I think he is an exceptional ambassador, not only for Everton but English football as a whole," Martinez added.
"It is almost a question of keeping him away from the training ground because he is so eager to improve himself."
The result means that Everton move up to fourth in the Premier League table and remain unbeaten after six matches.