I'm residing in Beijing but no Chinese passport, should I apply for the TAR visa in order to visit?

I'm currently studying in Beijing and would like to visit Lhasa during february. I don't have a Chinese passport but my country (Mexico) goes along the HongKong temporary visiting policy for 90 days. I'm trying to figure out the documents I need for the trip and found out about the visa. The information is a little bit misleading, maybe someone can help me out.