The idea is very simple: create a widget and configure it with the information you want pre-filled in your email.
Then tap the widget to start a new email with the configured information.
As simple as that.
This app is open-sourced on github, feel free to poke around in the code --> https://github.com/theyann/oneclickonemail
Contact me if you have ideas to improve it, or if you just want to say hi :)