I’m now an "Oleh Chadash" and in the Ulpan, talking about Chanuka, the teacher said that lighting the Chanukia was not "Chova" but tradition, since some of the pupils didn’t agree, we decided to check it with you, could you please help us?

Lighting The Chanukia is certainly a Mitzvah that is "Chova", which is written in the Shulchan Aruch, and not just a voluntary tradition. I'm not sure how this mistake you've mentioned has occured. The Rambam even states that "there is no Mitzvah dearer to Yisrael than lighting the Chanukia". Happy Chanuka. Rabbi Ro'i Margalit