There are some books on Zoroastrian religion, history and language to which a link is provided here:

1. Outlines of Parsi History, Zoroastrian Religion and Ancient Iranian Art (Condensed and Edited version of Outlines of Parsi History by H.K.Mirza) by Ramiyar P. Karanjia  https://www.yumpu.com/en/document/read/12403718/outlines-of-parsi-history-ramiyar-karanjia
2. In Search of My God           http://www.insearchofmygod.com/book/In-Search-of-My-God.pdf
3. Teach Yourself Avesta language by Ramiyar P. Karanjia http://www.avesta.org/language/Combined_Avesta_Grammar.pdf
4. My God Ahura Mazda – Children’s Primer and Activity Book by Ramiyar P. Karanjia  https://www.yumpu.com/en/document/view/12404103/my-god-ahura-mazda-ramiyar-karanjia
5. Khordeh Avesta ba Maeni (in English) by Kavasji E. Kanga        http://www.avesta.org/kanga/ka_english_kanga_epub.pdf
6. Serialised Stories from the Iranian Epic Shahnameh – PESHDAD by Ramiyar P. Karanjia https://www.yumpu.com/en/document/view/7277083/serilaised-stories-from-the-iranian-epic-ramiyar-karanjia/5