Fractures
Zuko realizes his destiny much earlier. As in, as soon as he wakes up in the palace after his Agni Kai and is told he is banished. Unfortunately, he's never been a patient one. So he storms right up to Ozai and tells him what he's going to do. And gets locked up for over three years. Then, one day, he's being pulled out and told he's the new Fire Lord.
A "Zuko never meets the Gaang and suddenly becomes Fire Lord after three years of literal torture" AU. In which the Gaang doesn't know what to think of the new Fire Lord who happens to be the missing nephew of Aang's firebending teacher, Iroh constantly has a headache, and, sure, maybe the world hates the Fire Nation, but the Fire Nation LOVES Zuko, and he can work with that.