Sunday dinner, Monday lunch in D.C./Baltimore
Well I can't really speak to the Baltimore area and you kind of gave us limited info (no area requests, price range, type of food etc).
If it was me I would try to get into either Equinox, Hook, Palena, or Proof for dinner. For lunch you should try to check out Central, Brasserie Beck, Acadiana, Jaleo or Bistro Bis. All are great restaurants (and some are actually open for both lunch and dinner.