The Ministry cafe does a surprisingly nice egg salad on Tuesdays.
If you haven't other lunch plans, I suggest you try it. Perhaps around half past eleven, before the place gets too terribly crowded.
You wouldn't want to miss the sandwiches, after all. I expect they'll be gone by quarter past noon. And you'll want a little time to savor it. Not too long. Certainly not enough for your superiors to mind. I do know the value of eating quickly, thanks to the demands of Mysteries.