[Vala] Call default mail app (like evolution) from a Vala/Gtk+ app

[Andres Fernandez <andres softwareperonista com ar>]

Hello, I'm trying to find how to call the window to write a mail of the
default mail app, with a predefined subject and a predefined text in the
body of the mail.

Is it possible?

My English is quite limited do I don't know if it is clear.

Thanks!