Fly to Iran and get a 30-day on arrival visa at the airport. This kind of visa is issued for 98 nationalities excluding USA, England, Canada, Colombia, Pakistan, Afghanistan, Iraq, Jordan, Bangladesh, and Somalia. If your nationality is among the countries authorized to get it, you can collect your visa against offering your passport, a passport-size photo and pay the costs depend on your nationality(20-170 USD). Usually there is no need to fill in any form beforehand but at the moment you need to receive your Iran visa invitation letter from and authorized travel agency so that you can get your visa on arrival.

You can check the Iranian visa process here.