A free online course about nutrition for mental well-being was discussed on RNZ. Click on this link and then the one in the RNZ article. The course through the University of Canterbury is free but if you wish to have certification to say you have completed the course, there is a fee of US$149.

https://www.rnz.co.nz/national/programmes/nights/audio/2018811251/online-learning-booming