Speaking to the Evening Standard, Martinez hailed Southgate for creating a "culture" within his squad.
"For me, obviously, I am on the outside looking in, and what I see is Gareth Southgate has brought all his success from Under-21 level and has developed an England culture," 44-year-old said.
"I think there is a clear structure, there has been a real tactical awareness, there has been a change of system to go into different qualifying games.
"They have found a system that suits this generation. There is a youth about them, an energy, a belief and a real desire."
Belgium are joint-top with England on six points going into Thursday's decider.