There are manufacturers such as Huf Haus that make very high quality (luxury) prefabricated homes[1]. They feature all the modern fittings you could want, and they are installed in the factory not on site. There was an episode of Grand Designs which featured a Huf Haus[2], it was constructed in a week on a concrete slab.

[1] https://en.wikipedia.org/wiki/Huf_Haus

[2] https://www.dailymotion.com/video/x2go2ld