I’m not sure if a voronoi generator is in Krita yet. There is/was a Google summer of code project going on to bring all sorts of patterns to Krita, but it may not have been integrated yet.
David Revoy wrote a bit about it here: Procedural texture generator (example and wishes)
In the second and third images you can see voronoi patterns being used. In the third image as light diffraction pattern like you want to do.
As for tutorials, I don’t know. I may have some time to experiment and do a quick write-up tomorrow if I succeed. But no promises! 