Ground rules: The term Green Lantern can be applied to any one of the policing power ring slingers across the Galaxy. In this fight the Green Lantern in question is the most well known GL of Earth, Hal Jordan.
Goku is the most powerful Sayian in the Dragon Ball Z universe. Like fine wine, he only gets more powerful with age and training, so although he may outclass GL today, I'm using the Goku from when I was familiar with the show: the Goku from the Cell Saga. The arena is a canyon surrounded by a mountain range and wide-open desert. These guys need their space.
Personal bias: Dragon Ball Z was a fun show. I always liked the energy-based heroes/villains and DBZ had no shortage of them. Speaking of energy, GLs power ring is far and away my favorite concept for a superhero. I can't say Hal Jordan is my favorite character, but if I could be any hero, it would be a Green Lantern.
Fight! Green Lantern powers up his ring and takes to the sky. He doesn't gain much altitude, just enough to see over walls of the canyon. He lands once he secures high ground. No sign of Goku. ...