Is there a way to add items to the 3D Viewport Pie Menus

I want to be able to add my own addon to the menus that appear through the included 3D Viewport Pie Menus. Anyone got some pointers as to where I should look for documentation for the Pie Menus addon?

the following link from latest blender manual provides information about “3D Viewport Pie Menus”

hope it helps.

I’m not sure about documentation but often it’s best to go directly to the source code:
Maybe you’re already digging into these?

There’s a basic template here:

This looks like what you want:

Good luck