This is unlocked in the exact same way as in the other editions of Minecraft, except Ghasts seem to spawn much less frequently in the Windows 10 version. Because of this, you'll have to spend a good amount of time exploring until you find one (remember to mark where you've been with torches, glowstone, etc. to avoid getting lost).
Once you have entered the nether and have found a Ghast, simply wait for it to shoot a fireball at you, then left click your mouse to deflect it with your sword back right as it's about to hit you. The Ghast should die in one hit, granting you the achievement.