What is the ruling on a woman teaching men the Holy Quran and its Tajweed in the presence of a Mahram?

If a woman adheres to the hijab and there is no seclusion (khalwa) or softening of speech, then there is no harm in her teaching adult males. However, it is preferable for her not to teach them. As for the practical aspect which relies on performance and instruction, reciting the Quran involves melodious chanting and beautifying the voice. It is disliked for a woman to raise her voice in recitation in the presence of non-mahram men, because her voice might be considered 'awrah (something that must be concealed) if it involves stretching and softening. Therefore, it is advised to avoid women teaching men in general, and specifically instructing them in Quranic recitation.