Mark-Paul Gosselaar -- The Shirtless RIPPED Tide

Attention Bayside High alumni: Zack Morris is jacked!

Zack -- aka Mark-Paul Gosselaar -- showed off his lean, smooth and ripped 39-year-old pecs, bis and abs, while filming a surfing scene with his "Franklin & Bash" co-star Breckin Meyer and Eric Balfour in Malibu on Tuesday.

These days he's saved by the dumbbell.