High
I think there may be an error in the manual (if you were using that for reference)
Whilst the LemurMenu page lists 'content' as the attribute it's actually 'items'
So the scripting would be - setattribute(Menu, 'items', {'opt1', 'opt2'});
And sent via OSC it is - /Menu @items Opt1 Opt2
There is a handy internal function called 'getattributelist' that can report an objects attributes . . .
The manual does indeed have an error. I spent about half an hour puzzling over this last night. A search of the forums turned up an example of the correct attribute name, "items." Kind of frustrating when you dutifully RTFM, but get the wrong answers there.