If they're any good at it, you won't know who stole your food. If I did know who the thief was, yelling/cursing/threatening would get me fired. It's easier to keep my food at my desk in an insulated lunchbox with an ice pack.
And finally, HR doesn't give a flying fuck about your lunch. They would laugh in your face if you threatened to sue them.
Not familiar with the acronym "EI"