After the plugin has been fired, a series of custom events are available for the menu. The open and close events come in an infinitive, a participle and a past participle form.
The infinitive (e.g. open) can be triggered for controlling the menu manually, the participle (e.g. opening) is triggered when the action is actually executed and the past participle (e.g. opened) is triggered on the completion of the action.

All custom events are bound to the .mm-namespace, so triggering (or binding a new function to) an event would best be done like this:

$("#my-menu").trigger( "open.mm" );
$("#my-menu").on(
   "opening.mm",
   function()
   {
      alert( "The menu will now be opened." );
   }
);
$("#my-menu").on(
   "opened.mm",
   function()
   {
      alert( "The menu has just been opened." );
   }
);

Click the menu-button in the header to open the menu and have a look at all the events.