The Belgium international scored deep into injury time at Goodison Park last week to send the third-round tie to a replay after James Collins appeared to have put Sam Allardyce's men through.
Lukaku - a club-record signing during the close season - followed up that leveller with an impressive display against Premier League champions Manchester City as Everton again struck late to salvage a home draw.
Despite impressing regularly on loan at Everton last term, he has struggled to make the same impact since completing a permanent move - with Lukaku failing to score in the six matches before Tuesday's FA Cup draw.
The 21-year-old was benched for the defeats to Newcastle United and Hull City but, ahead of the trip to Upton Park, Martinez feels Lukaku is back on track.
"Throughout the [City] game, I thought Romelu looked back to his best from a physical point of view," the Spaniard told Everton's official website.
"When he has that pace and power with the quality that he has, he becomes really strong for us.
"You can see when he faces people one on one that he is really sharp. He was a really good outlet and a good threat.
"It's a sign of what's to come in the second half of the season."
West Ham also drew 1-1 on Saturday after Andy Carroll's superb first-half strike was cancelled out by Mark Noble's own goal against Swansea City.
With Allardyce having missed the game due to a chest infection, assistant Neil McDonald took charge, although the former Blackburn Rovers boss is expected back on the touchline at Upton Park this week.
While Carroll offered a reminder of his presence up front at the Liberty Stadium, Allardyce and McDonald may again be without leading scorer Diafra Sakho due to a persistent back injury.
"Sakho [has] the back injury but Enner [Valencia] has come up top and played with Andy and that gives us that little bit of change into feet through Andy or in behind with Enner," said McDonald.
"It didn't work as much as we thought it should have done but it worked.
"I'm not 100 per cent sure [whether Sakho will be fit for Tuesday], his back is still sore and he's having treatment and we'll reassess it as time goes along.
"We need to make sure all the bumps and bruises clear up. We'll be focusing on the Everton game straight away and will be looking forward to the game and looking to win the game."
