Some are AU, some fit with canon. You can sort out which is which.
Five Buildings Zuko Didn't Burn Down
The House of Aila
The island house in summer, age 4:
When Zuko was a boy—a bare spit of a thing, with skinny white arms and eyes more bronze than gold—before his sister went mad or his cousin went dead, he caused a fire that destroyed priceless family artifacts and turned his grandmother Aila's birth house to cinders. As long as he lived, beginning that summer on Ember Island, Zuko was forever destroying the history and the accoutrements that he loved. A summer retreat, a library, a royal palace, looming gates that barred his uncle from the throne: eventually, the prince would raze them all. But that was the future, and when the home on Ember Island caught fire he was a boy like any other in his nation.
It happened in the quiet rustle of night and bed sheets: he tossed and turned, he shuddered and thrashed. Mere days had passed since the fire manifested in Prince Zuko's hands, and now the power crept along his veins, through his dreams, and out into the world. The curtains around his mattress caught first, then the bedside table. Flames leapt to the walls, to the window dressings, and the crown prince woke to a world of gold and orange. He didn't stop the fire—he had not the strength or the knowledge—but nor did he cry out for help. He could have wept for his mother, or screamed for a servant, but in the end Zuko did what lonely boys do: he ran, and he hid, and he waited for the flames to disappear or to eat him alive.
It might have been hours or it might have been minutes before his father found him, terrified and only four, shut in a kitchen cabinet and light-headed from smoke. Ozai plucked his son's pale body—white and black and bronze, limbs and pajamas and fright—from the shelter of the cupboard, carried him through the burning wreckage, and promised without words that there was nothing to fear in this world.
The estate's remains smoldered, the royal family left, and Zuko never stepped foot on Ember Island again. The home of his grandmother had burned, as one day the home of his grandfather would. It was almost prophecy, if anyone had cared to see it as such—though of course, at the time, none did.
Zuko was only a child, a boy with a fire dream, and there were plenty boys at that age. Not for many years would he become a man with a fire's hunger.