It's the PLAB test I think he needs to take and pass. I gather it's not easy, nor cheap to take however.
If he takes this test then my understanding is that he would then be a doctor qualified to practice in the UK (subject to having leave to remain for this purpose obviously).
Tier 1 out of country application are closed obviousy, so he would have to apply as a Tier 2 Skilled Sponsored worker. In order to do this we would need to do a job on the shortage occupation list:-
See the section on medical practitioners and those areas listed under Non-Consultant, Non-training, medical staff posts. He would require a job offer from an employer licensed to sponsor Tier 2 migrant and would also need to meet the points-based systems requirements in terms of points for elibility:-
He should be able to apply with his travel document.
The difficulty is that the UKBA will be on an adversarial footing from the time of application because they will take the view that as he is a refugee when and if his visa is to expire and he does not/can't apply for an extension he will be a risk of an overstay.
In view of the complications it really would best to instruct a solicitor to prepare his application for him if he can find a licensed sponsor willing to offer him a job.