Zuko studies Toph’s Earth Bending and starts to develop his own move similar to Uncle Iroh’s lighting redirection. He calls it Lighting Dispersion. In basic terms. He uses his own energy to out stubborn the lighting and makes it explode before it can get into his body. Much like when an Earth Bender makes a rock explode when he or she punches it. When he faces against Azula for the crown he is forced to use that move when she targets Katara. He quickly grounds himself, centers his energy and punches the lighting like Toph would have. And it works. Azula is shocked back into sanity because Zuko just stopped a Comet powered lighting bolt by punching it and just gives up because there is literally nothing she can do to top that.