I've never heard of Aztec soup but looking at the recipe I found, it should be very easy to veganize.
Use no-chicken broth for the broth
Use a light seitan, morningstar chicken strips or gardein chicken for the chicken
And you can even add vegan sour cream or look up a crema recipe using soy yogurt (Isa has one somewhere, it is basically soy yogurt and lime juice I believe)http://www.cookingchanneltv.com/recipes ... index.html
Ida also has a really good tortilla soup recipe, I think it is in AFR.