Current Belgium boss Martinez takes on Mexico and record goalscorer Hernandez this week in an international friendly and is looking forward to the challenge.
Martinez admitted he wanted to manage Hernandez but the opportunity never presented itself.
Martinez told ESPN: "We've always followed him very closely because he's a player that surprised us a lot with the way he adapted at Manchester United and the way he finishes moves.
"He's a player with so much intelligence with his movement. It was never possible [to sign him], but yes he's been one of the players that we've followed closely."
Manchester United did sell Hernandez in 2014 to Bayer Leverkusen, at a time when Martinez was still Everton manager.
The Toffees did have Romelu Lukaku at the time and so the need for a striker was not as pronounced as their current situation.
Hernandez signed for West Ham in the summer from Leverkusen, and would have been a smart addition for the forward-needy Toffees.
The 29-year-old has four goals in 11 appearances for the struggling Hammers this season.