The Scandic bunker landside should have some sort of "lobby bar". Also the Airport Hilton. The only restaurant I would currently eat at is the landside Fly Inn upstairs from departures.

As for area restaurants, the Flamingo entertainment complex at the Jumbo shopping mall has a few passable ones open until 10 pm or so on Sundays. Around five minutes by cab from the terminal.

http://www.flamingo.fi/en

A new "restaurant World" is due to open in the extension wing in August.