I'm working on a story where the characters are stranded on a planet that turns so incredibly slow that it acts like a tidally locked planet, with one side burning and the other frozen. However because the planet still turns, the characters are forced to out-walk it constantly in the habitable strip, chasing the sun. I can't find anything on the internet that even mentions something like this, so I was wondering if a place with this environment is possible.
Yes! In fact, we can find it right in our solar system.
Mercury is the closest thing to what you would want. It is in a 3:2 spin-orbit resonance, meaning 3 Mercurian days happen every two Mercurian years. Since it has no atmosphere, there is very little heat distribution going on at the surface, so the day side is scorching and the night side is freezing.
Another example of a planet with very long days is Venus, though it does not have a spin-orbit resonance, the atmosphere does distribute solar heat, and all of the surface is a scorching wasteland, not just the day side.
In conclusion, your planet needs to have
No real atmosphere
Reasonable distance to the sun (so it can actually be hot enough to be deadly)
Very long days