To look at what other folks have said about Lewis and his treatment of race and Orientalism in the Narnia books, you could check out:
Are The Chronicles of Narnia Sexist and Racist?
Red Dwarf, Black Dwarf: The Racial Overtones of Narnia
C.S. Lewis' Calormen: Exacerbating Ethnic Tensions?
So Why is She the White Witch?
For another look at Narnia with an eye towards concerns about gender and sexuality you might be interested in the short story, The Problem of Susan by Neil Gaiman.
fictional works using settings created by other artists