Deletion is never a good first option, you have none left.
The only way to recover deleted files is through an application to recover deleted files (google that, there should be plenty of options, many free). The longer between deletion and any recovery attempt, the less likely the success rate.
You would also have to know what it is that you seek to recover (date, time of deletion roughly) as there could be hundreds of hits in its search for deleted files. Avast may well alert when trying to recover these files, if so sending to the chest is the best/safest option.
Look in the C:\Documents and Settings\All Users\Application Data\Avast Software\Avast\report\aswBoot.txt file (XP location) C:\ProgramData\Avast Software\Avast\report\aswBoot.txt (Vista, Win7 location), check this file using notepad for info on the scan/detections, etc.
Copy and paste that information, file name, location and malware name of the detections. That gives us something to work with (and also when you attempt to undelete these files), to say what the likelihood of the detection being good.