That is part of the frame and the impact bent that piece. Fixable, IMO, yes but it would need to be reienforced in someway once its straighten. It probably needs to be banged/hammered back then a piece of steel on both sides welded and welded to the frame/body of the vehicle. Once its straighten, the rear tires should be back to normal instead of sticking out one side more then the other like it is now.