The Phoenix Emperor
Based on a conversation Nichya and SignlessAcolyte had where Azula finds Zuko at the Jasmine Dragon instead of Katara.
Aang found enlightenment far too quickly, even for a monk, even for someone whose spirit has gone through this process 10,000 times already. That means he has his vision a week after they overthrow yet another government. More plot as it becomes relevant, but the point here is: now Zuko and Azula have time to interact before Aang crashes the party.
- Part 1 of The Phoenix Emperor
The Fire Siblings have taken over the Earth Kingdom, but Ozai still sits on the Dragon Throne. After having left several parting gifts, Zuko has left to begin the next phase of his plan: Teaching the Avatar firebending, and in the meantime getting him to dispose of the current Fire Lord.
In the meantime, Azula finds herself in hot water with her father, suspicious of her for her part in "killing" the Avatar.
- Part 2 of The Phoenix Emperor