It's looking like a "Baywatch" girl summer for Megan Thee Stallion ... 'cause she was just spotted showing off her body-ody in a bikini on set!!! Check out the footage ... the rapper hit the sand in Long Beach in an orange and white bikini paired with a matching sarong ... and it looked like she was feeling herself as she flaunted her rock-solid abs while cameras were rolling. Her cameo here may involve a musical number too ... 'cause eagle-eyed fans spotted a Megan Thee Stallion stage on set.