For me, it was complicated by the fact that I had never met my GP before. She wanted to do the full intake interview, but I just sat down and said, "Hi, I'm <legal name> and I am pretty sure I am transgender. I'd like a referral to a psychologist." I could tell it was the first time she had heard that!
I would have skipped the GP altogether and self-referred to the psychologist, but I needed the referral letter so that my insurance would cover it. I had actually already self-referred to the mental health unit in the public system and had a psychologist's appointment already scheduled, but it was so far in the future, that I wanted to go private to speed things up, hence the need for insurance coverage.
I got my referral letter and then she covered the intake interview stuff.