As someone who is stuck with a "junior developer" who hasn't produced a single line of working code during past 1.5years in my team the "one interview and done" isn't working these days.
Only way to fire someone on the spot is if they are breaking law or refusing to do the work
If this person is literally not producing anything useful, then set them a basic piece of work and tell them to complete it. If they can't give them a warning, tell them to upskill. Repeat after a month. And again a month after that. If they still can't do it then you have plenty of evidence to justify firing them, anywhere in the world.