El Charro can best be thought of as an option of last resort for vegetarians and vegan. I went there with some friends who are meat-eaters. When I asked which were the vegan options, the choices were either a salad or a chimichanga made specially by the chef. I chose the chimi. It contained vegetables and whole beans (not refried beans because my server told me they were not vegan).
The chimichanga was delicious. The waitstaff were very helpful. I was very grateful to the chef for making such a nice meal for me, and I'm giving the restaurant two stars to recognize their great service. However, my goal here is to give El Charro's a rating that reflects its suitability for vegetarians and vegans. It's true that there would have been more options if I were a lacto-vegetarian. However, given the limited choices for vegans, I really can't give it more than two stars (and it really only just squeaks that second star because the staff were so resourceful).
I would certainly go back there in a pinch, but my first choice for veggie-friendly Mexican food in Tucson is La Indita on 4th Avenue.