United Mileageplus Dining members (and if you aren’t one you should be — it’s free.. and lots of other airlines offer the same deal) earn 500 bonus miles automatically for eating at three participating restaurants by October 31st.
(Edited to note that the link above for 500 bonus miles doesn’t work unless you’re first logged in at My Mileageplus. That’s okay — just take my word for it. You don’t need to register for the promotion if you’re already registered for Mileageplus Dining.)