Hook kicks and spinning hook kicks are 2 different techniques... If you mean spinning ones, there are lot of examples. If you mean simple hook kicks the only two i can remember in MMA are:
(That was one of the most ugly, awkward technique i have ever seen worked)
In teakwon-do and some karate styles, it's a lot more common:
As for technique, it's kinda like throwing a side kick, but your target is right next to the face... And when your leg is stretched, you hook it using the knee across his face. You also use your hip to add power, moving in the opposite way you would do with a roundhouse, but a lot of times, for a clean technique in demos, it's just the knee doing the job.
You want to impact with the heel.
And most of the time you must step in, before you throw it, it also adds power.