zsh: Command not found: nodemon
sudo npm i -g nodemon
This command installs Nodemon globally and you can access it in any project.
Note: Sudo is for Mac users, like myself, to get access to save things to password protected areas on the computer.
After having it installed globally, instead of locally in my project, I could run this command in the Terminal and the app started to run and listen to my changes:
If you have come across this same problem I hope this solution works for you too.