The 45-year-old UFC Hall of Famer says he got the call recently after watching some of the new Tyson training videos and believes a tilt with Iron Mike could be "the opportunity of my life."

Ortiz -- an MMA legend -- says he doesn't know if Mike is interested in boxing or a mixed martial arts fight ... but he's down either way.

Tito says he's been boxing for 20 years as part of his MMA training and thinks at this point in their lives, he's better in the ring than Mike who hasn't been in a pro fight since a 2005 loss to Kevin McBride.

Of course, if you've seen the new Tyson training videos ... he looks damn good for a 53-year-old.

"Has Tyson been punched in the face in the last 15 years? No he hasn't. And I have and I've been able to subdue everyone I've competed against over the past 4 years."

It's true ... Tito's on a 3-fight win streak with victories over Chuck Liddell, Chael Sonnen and Alberto Del Rio.

Tito says thinks a Tyson vs. Ortiz fight could DOUBLE the numbers Mayweather vs. McGregor did ... calling it "an amazing opportunity for both of our brands."

We spoke with Mike about the possibility of a Tito fight recently -- and he said he's down to fight everyone as long as the money goes to charity ... but it's clear nothing is in stone yet.