Steve Nash: I'm Engaged ... To Smokin' Hot Volleyball Player!!

Steve Nash is officially on the road to marriage ... proposing to his super hot volleyball player girlfriend ... and she said YES!

Nash, 42 -- who retired from the NBA last year after playing 19 seasons -- popped the question to his GF Lilla Frederick, 25, at a resort city in Majorca, Spain.

Frederick was a stud volleyball player at Pepperdine University.