For secondary school your CPA qualification is recognised by the Teaching Council. For details on courses recognised see www.teachingcouncil.ie and look at the link to registered courses on their homepage.
You would need then to do the H.Dip in Education which is one year full-time in most universities but you can do it over 2 years part-time. Check out DCU and Hibernia College (www.hiberniacollege.net).
Best of luck with your choice and please let me know if there is anything else I can help with.