This is, I think, an initial phase bullethead parrotfish. Parrotfish can go through several phases and look quite different in each one. Some also change sex.
So why is this titled ‘crunchy parrotfish?’ Well, I was watching this fish feed and when it feeds, it uses that big, white-rimmed beak to scrape algae and coral polys off the rocks. While it was doing so, I could clearly hear the quite loud crunching noise it made.