What is the easiest way to add a custom icon to an application using monodevelop? [duplicate]

Answer 1

Go to the Project Menu -> <project name> Options and in the project option windows :

Answer 2

Right-click your project, Options, select the Build/General page and provide a Win32 icon.

Note that the icon will probably only show up on Windows, Linux uses a different way to display icons for executable files (can't help you here though).