We're told Mark and Jason struck up a friendship over the last 6 weeks while they were both in Australia -- Mark training for his fight against Derrick Lewis, and Jason filming for "Aquaman." They've been working out at the same gym called Heartbreak.

As a good luck gesture for Mark's fight next month in New Zealand, Jason -- as well as cast and crew and some of Hunt's training partners -- performed that country's traditional war dance ... the haka. Jason and Mark are both of Samoan descent ... from where the dance originates.

Jason will be attending Mark's fight.

Anyway, from the looks of these vids ... Mark wasn't expecting the whole shebang. Surprised much?