Gisele Bündchen, Jiu-Jitsu Instructor Joaquim Valente Back in Costa Rica

Gisele Bündchen and her jiu-jitsu instructor are reunited in familiar territory -- her home in Costa Rica, and she's giving him a peek at what her ex, Tom Brady, might be missing.

Gisele showed off her perfectly toned abs Monday as she got in some exercise with Joaquim Valente ... venturing out on a walk with a couple of super cute pups. We know GB retired from modeling years ago, but those abs still scream supermodel.

Costa Rica's fast becoming a favorite destination for Gisele and Joaquim ... we saw them down there a couple months ago, when they were riding horses together through the jungle.

Of course, Gisele and Tom used to frequent CR when they were married ... for family trips and romantic getaways -- but now it seems Joaquim is enjoying Gisele's slice of paradise. We're referring to her property down there.

The trip to Costa Rica would seem to lend more credence to the thought Gisele and Joaquim are more than just friends or jiu-jitsu buddies ... but they're still not making anything official. Or unofficial, for that matter.

Gisele's camp's been claiming Joaquim tags along on family trips to train her and her kids ... but they do a lot of things without the kiddos that, at least, look couple-y.

Costa Rica seems to be Gisele and Joaquim's territory now. But, Tom's got his cats!!!