I think it's impossible for us to advise. Your teacher's objection seems to be not so much the wording ('Of becoming a teacher' is OK - though I'd prefer just 'Becoming a teacher' ['Of...' is reminiscent of Dickensian chapter headings]) as the scope: 'Becoming a Teacher' is a very big and diffuse topic, and your teacher may want you to concentrate your focus a bit. Something like 'Becoming a teacher: difficulties specific to aspiring teachers from the Philippines, and the benefits of a background in Tagalog as well as Spanish', perhaps. Or maybe your teacher wants you to name a subject that you can tackle realistically within the given word-limit or time constraints. Only your teacher will know what s/he wants.
Student or Learner