So here's a Zuko tutorial. Its a very literal tutorial, rather than making Zuko look realistic like I normally would, this is more of a cartoony version, its not my favorite, but some people might find it helpful/interesting.
Supplies! (I'm feeling lazy, if you have questions as to what is what, just ask)
Block out your eyebrows with eyebrow plastic and flexible sealer (spirit gum will also suffice), then add your cotton and latex burn. Then, add creme foundation. Be sure to block our your lips, don't bother putting the makeup on the burn just yet, there's going to be another color on it.
Using the brightest red in a bruise and burn wheel cover the burn the best you can (its goign to be difficult, latex does not like to be covered - at least the kind I used, which is cheap and bad) then around the eye socket, use a dark maroon.
More colors, add some shadows to the burn to make it 3 dimensional, highlights are also a good idea here too. I also covered up part of my eyebrow since I couldn't get it to block out as well as I would have liked.
Now your highlights and shadows! Which isn't 100% necessary for cosplay purposes, at least nothing this dramatic. I usually contour my nose (since I have a honker) and hollow out my cheeks, since I don't have much in the way of definition there. But instead of a dark brown creme I use a midtoned brown eyeshadow on top of my concealer. Works just as well! Also add your grumpy brow line and manry eyebrow. Which I did because I've some some pretty girly brows, but this is FAR cartoonier than you would want for things like cosplay. For stage this would read just fine.
I ended up making it black, because apparently I forgot my hair was black. I don't know how that happened. But there we have it.
And the other side.
When you peel the burn off it looks pretty silly.