I would speculate it's a derivative of John - see names like Ivan or Yves, and that it's much more likely to be Celtic than Hebrew.
Evans is an extremely common Welsh surname. I was recently involved in a research project around the life of one George Heaven, and can confirm that the number of Heavens/Evans's on the Welsh border - including in Bristol, Gloucestershire and Shropshire - is phenomenal.
It's a Welsh name. British at a push. I'd put it as unlikely to be Jewish, but someone else might have more evidence.