To earn a gold medal, you must complete the Hunter Tutorial within six minutes. This is a slightly easier than the Monster Tutorial because there is more time. On a good run you can complete it in around five minutes. Repeat the tutorial a couple of times until you know it well. The hardest part is at the end when you have to fight the monster. Just keep shooting it with your lightning gun and assault rifle until it is defeated. Always activate your shield when the monster is about to attack you.